[ BUILD # : 200909080527 ]
[ JDK VERSION : 1.6.* ]
I have a project group that I created to hold a specified project. I
then renamed that project and checked the option that said that its
associated directory should also be renamed. I switched to another
group and then back again and found that the project group was empty.
The project has become disassociated with the group.
After a little digging I noticed that the project's properties file
had properties that still specified the old project name and
location. These properties should be renamed as a part of the
project rename refactoring. Additionally it would be consistent if
the project group was renamed to match the new project name.
I'd like to NetFIX  this bug. Is it possible? 
It would indeed be better if the org.netbeans.modules.project.ui.groups.AdHocGroup (I assume this is the type of group
you were using) tracked project renames/moves and updated its metadata accordingly. Tricky because there is no API for
listening to project renames/moves; DefaultProjectOperationsImplementation could provide a static event set which
AdHocGroup could add a static listener to (taking advantage of the projectui -> projectuiapi impl dep).
Renaming the project group is not a good idea; in general a group contains many projects.