start C::B from the console, also you start it with --debug-log option (this one adds a second logging window with some debugging messages)
Nothing in the Debug log. But I just noticed, that the log window already has a log tab for Code::Blocks and there is indeed a message:
/usr/local/lib/codeblocks/plugins/libwxsmith.so: not loaded (missing symbols?)
/usr/local/lib/codeblocks/plugins/libwxsmithcontribitems.so: not loaded (missing symbols?)
No problem actually, since I don't use wxsmith (though it would still be nice to get rid of this message).
settings -> env settings -> view -> auto show/hide message pane -> keep after build errors
if the message pane is hidden you could show it from the view menu or by hitting f2
The settings were correct in the first place. But I think I found the problem. The build process ended with a summary of 0 warnings and 0 errors, so I guess Code::Blocks thought everything would be okay and it could hide the window. But there were additional error messages afterwards, that weren't counted. Unfortunately I don't have the old project file anymore, which triggered this problem (resulted from porting a project from Windows to Linux).