I'm guessing the SLSB method that loads a group config is not smart enough to fetch live configs for member Resources; it probably just tries to load persisted configs and if none are found, returns empty configs (when I attached to coregui w/ JPDA, I saw that the member configs were empty, not null).
To load group member configs, call configurationManager.getResourceConfigurationsForCompatibleGroup(), rather than configurationManager.getResourceConfigurationMapForCompatibleGroup(), to ensure we get the latest/live configs for each of the group members - [master ed17448].
[master eac0b5c] removes getResourceConfigurationMapForCompatibleGroup() from ConfigurationManagerLocal and ConfigurationManagerBean, since it is not a method anyone should ever call (getResourceConfigurationsForCompatibleGroup() should always be used instead).
To verify this fix:
1) create a compatible group of some type of Resource that support configuration (e.g. RHQ Agent, Datasource, Topic, Queue, etc.). make sure that you have not gone to the Configuration>Current subtab for any of the members of the group.
2) go the group's Configuration>Current subtab, and make sure the group's config is displayed. change the values of a couple properties, then save the group config. verify that succeeds.
3) make some changes to one of the group members configs *outside of the RHQ GUI or CLI*. for example, if it's a group of RHQ Agent Resources, change some Agent config props from the Agent command prompt.
4) go back to the group's Configuration>Current subtab, and make sure the group's config is displayed and the updates you made in step 3) are evident. this verifies that the group config always represents the "live" configs of each of the group's members, and not just the latest member configs from the DB.
Created attachment 499871 [details]
server log showing error during verification process
Verified on rhq-server-4.0.1-SNAPSHOT Build# a104cdf
My setup was on postgres. I do not see the error message that Michael saw in comment# 6.
The UI change reflected correctly,
2011-05-20 17:13:58,450 INFO [org.rhq.enterprise.server.configuration.ConfigurationManagerBean] Group Resource configuration update  for ResourceGroup[id=10031, name=compact group, category=COMPATIBLE, type=RHQ Agent, isDynaGroup=false, isClusterGroup=false] has completed with status [Success].
The Agent command prompt change also reflected correctly on the UI,
> setconfig rhq.agent.wait-for-server-at-startup-msecs=50000
Set preference: rhq.agent.wait-for-server-at-startup-msecs=50000
I'm marking this bug as verified. Will double check with Michael separately.
Bookkeeping - closing bug - fixed in recent release.