After upgrade to 1.18.2 hostgroup parameters are not overridden when using Image based Provisioning Method. It's working correctly for Network Based Provisioning Method.

Env:
Version 1.18.2
ovirt computer resource: RHEVM 4.2.6.4-0.1

Repro steps:
1 - create new host
2 - pick hostgroup
3 - choose Imaged Based provisioning method
4 - override some parameter (in this case cumulative_patch_url_pre_install was set to true, default value is false)
5 - submit

Relevant part of finish template:
<% if host_param("cumulative_patch_url_pre_install") -%>

1. this patch will be applied on not yet installed JON server
   export CUMULATIVE_PATCH_PRE_INSTALL=<%=host_param("cumulative_patch_url_pre_install")-%>
   <% end -%>

Result:
A default value is used for the parameter which should have been overridden.
It's visible in logs that cumulative_patch_url_pre_install should be overridden:
2018-10-31T07:26:31 [I|app|ede89] Parameters: {"utf8"=>"✓", "authenticity_token"=>"PRiwewC5bkXrlW5U76uFXYDk9ik292wDLR95UI31g0PBo+fDqU2YizcGrxyIj+81i/eEAbAl76OORIq9J5sewQ==", "host"=>{"name"=>"fbr-test2", "hostgroup_id"=>"59", "puppetclass_ids"=>[""], "managed"=>"true", "progress_report_id"=>"[FILTERED]", "type"=>"Host::Managed", "interfaces_attributes"=>{"0"=>{"_destroy"=>"0", "type"=>"Nic::Managed", "mac"=>"", "identifier"=>"", "name"=>"fbr-test2", "domain_id"=>"2", "subnet_id"=>"1", "ip"=>"10.16.23.203", "ip6"=>"", "managed"=>"1", "primary"=>"1", "provision"=>"1", "virtual"=>"0", "tag"=>"", "attached_to"=>"", "compute_attributes"=>{"name"=>"em1", "network"=>"00000000-0000-0000-0000-000000000009"}}}, "compute_attributes"=>{"cluster"=>"9895b86e-04d1-4c74-9d85-69f696088af3", "instance_type"=>"", "cores"=>"4", "sockets"=>"1", "memory"=>"4294967296", "start"=>"1", "image_id"=>"c5d6ca8f-c362-4a0b-848b-12801bea0531"}, "architecture_id"=>"1", "operatingsystem_id"=>"17", "provision_method"=>"image", "build"=>"1", "medium_id"=>"", "ptable_id"=>"", "pxe_loader"=>"PXELinux BIOS", "disk"=>"", "root_pass"=>"[FILTERED]", "host_parameters_attributes"=>{"1540985186262"=>{"name"=>"cumulative_patch_url_pre_install", "value"=>"[FILTERED]", "hidden_value"=>"[FILTERED]", "_destroy"=>"false"}}, "is_owned_by"=>"4-Users", "enabled"=>"1", "comment"=>"", "overwrite"=>"false"}}

But later when rendering the template - Unattended render of 'jon_shellscripts' = '2b4424ea43ddd8322de3375bbe514617a3d6bedbcbaee20a9482aa80afc210f8' the default value is used: | # this patch will be applied on not yet installed JON server | export CUMULATIVE_PATCH_PRE_INSTALL=false

What is confusing is that UI shows that the value was correctly overridden which is not true (the env variable on created VM was set to false), UI->Host->Templates->Finish Template->Review:

1. this patch will be applied on not yet installed JON server
   export CUMULATIVE_PATCH_PRE_INSTALL=true

Full production log attached