Here is the text I was pasting in:

<%#
kind: ptable
name: Kickstart default
oses:
- CentOS 5
- CentOS 6
- CentOS 7
- Fedora 16
- Fedora 17
- Fedora 18
- Fedora 19
- Fedora 20
- RedHat 5
- RedHat 6
- RedHat 7
%>
zerombr
clearpart --all --initlabel
part /boot --fstype ext4 --size=500
part swap --size=4096
part pv.01 --size=1 --grow --ondisk=/dev/disk/by-path/pci-0000:03:00.0-scsi-0:0:0:0
part pv.02 --size=1 --grow --ondisk=/dev/disk/by-path/pci-0000:03:00.0-scsi-0:0:1:0
volgroup root pv.01
volgroup data pv.02
logvol / --vgname=root --fstype=ext4 --size=1 --grow --name=lv_root
logvol /data --vgname=data --fstype=ext4 --size=1 --grow --name=lv_data

I just ran an 'yum update' and it autoupgraded. Was a previous 1.10.x latest. Was working fine. Tried installing the 'new' version on 'new' os and things just didn't work. I can't edit ANY templates that are related to partitioning, or even edit old ones.

I also did a 'fresh' install on virgin centos 6.8 (the currentest after update), and got the same results. but the errors are different. I haven't configured any infrastructure yet, just trying to edit the partition types w/o configuring the proxy.

[ 2016-05-03 21:22:27.7624 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] [ 2016-05-03 21:22:27.7622 3135/0x00000002769f10(Worker 1) utils.rb:74 ]: *** Exception EOFError in Rack application object (bad content body) (process 3135, thread 0x00000002769f10(Worker 1)):
[ 2016-05-03 21:22:27.7624 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/rack-1.5.2/lib/rack/multipart/parser.rb:117:in `get_current_head_and_filename_and_content_type_and_name_and_body'
[ 2016-05-03 21:22:27.7624 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/rack-1.5.2/lib/rack/multipart/parser.rb:19:in `block in parse'
[ 2016-05-03 21:22:27.7624 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/rack-1.5.2/lib/rack/multipart/parser.rb:17:in `loop'
[ 2016-05-03 21:22:27.7624 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/rack-1.5.2/lib/rack/multipart/parser.rb:17:in `parse'
[ 2016-05-03 21:22:27.7624 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/rack-1.5.2/lib/rack/multipart.rb:25:in `parse_multipart'
[ 2016-05-03 21:22:27.7624 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/rack-1.5.2/lib/rack/request.rb:377:in `parse_multipart'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/rack-1.5.2/lib/rack/request.rb:203:in `POST'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/rack-1.5.2/lib/rack/methodoverride.rb:26:in `method_override'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/rack-1.5.2/lib/rack/methodoverride.rb:14:in `call'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/rack-1.5.2/lib/rack/runtime.rb:17:in `call'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/activesupport-4.1.5/lib/active_support/cache/strategy/local_cache_middleware.rb:26:in `call'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/actionpack-4.1.5/lib/action_dispatch/middleware/static.rb:64:in `call'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/rack-1.5.2/lib/rack/sendfile.rb:112:in `call'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/railties-4.1.5/lib/rails/engine.rb:514:in `call'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/railties-4.1.5/lib/rails/application.rb:144:in `call'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/railties-4.1.5/lib/rails/railtie.rb:194:in `public_send'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/railties-4.1.5/lib/rails/railtie.rb:194:in `method_missing'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/rack-1.5.2/lib/rack/builder.rb:138:in `call'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/rack-1.5.2/lib/rack/urlmap.rb:65:in `block in call'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/rack-1.5.2/lib/rack/urlmap.rb:50:in `each'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/rh/rh-ror41/root/usr/share/gems/gems/rack-1.5.2/lib/rack/urlmap.rb:50:in `call'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /usr/lib/ruby/gems/1.8/gems/passenger-4.0.18/lib/phusion_passenger/rack/thread_handler_extension.rb:77:in `process_request'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /usr/lib/ruby/gems/1.8/gems/passenger-4.0.18/lib/phusion_passenger/request_handler/thread_handler.rb:140:in `accept_and_process_next_request'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /usr/lib/ruby/gems/1.8/gems/passenger-4.0.18/lib/phusion_passenger/request_handler/thread_handler.rb:108:in `main_loop'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /usr/lib/ruby/gems/1.8/gems/passenger-4.0.18/lib/phusion_passenger/request_handler.rb:441:in `block (3 levels) in start_threads'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/theforeman/tfm/root/usr/share/gems/gems/logging-1.8.2/lib/logging/diagnostic_context.rb:323:in `call'
[ 2016-05-03 21:22:27.7625 2637/7f6204169700 Pool2/Implementation.cpp:1274 ]: [App 2807 stderr] from /opt/theforeman/tfm/root/usr/share/gems/gems/logging-1.8.2/lib/logging/diagnostic_context.rb:323:in `block in create_with_logging_context'
[root@foreman-portable ~]#

I did open the window in a 'new' tab and the internal server error goes away. Looks like it might be related like you said.