OK, necroposting (love that term, all credit to its first user but I don't remember who that was).
A project edited (and maybe set ParentBackground to true and back to false ?) but has serious issues with, eg Lazarus 2.0.10
While its a pain when we find we cannot open that project in the IDE, its even worse if you build your app from the command line using, eg, the Laz 2.0.10 used by Debian autobuild. It builds fine, raises no errors but crashes on startup.
The 2.2 release notes perhaps need to mention that potential to silently make a non viable binary ?
Davo
Edit : and setting "Project Options->Miscallaneous->Maximize compatibility of project files" did not help incidently, has been set for some years.