I've found this problem (at least) in 1.1RC5 and 1.1

How to reproduce it:
- Create a hostgroup A with a parameter foo=bar,
- Create a hostgrup B whose parent is A.
- Create a host foreman-rules and assign B as its hostgroup.
- Now search for all the host that match param.foo=bar (using the web interface for instance). You will get an empty list.
- Overwrite foo param in hostgroup B or in host foreman-rules, the search works perfeclty.

It seems that I can only search for params that are defined in the host or in the hostgroup that it's assigned but not deep in the hostgroup hierarchy.