Sorry to bump an old thead, but I'm having a similar problem.
Running Linux Mint 17.2 Cinnamon 64 bit Lazurus 1.4.4
As JuhaManninen told me in another thread (My hello thread), I've got the "Show single button in taskbar" checked, but this is what my taskbar look like: (Attached).
I've tried restarting Lazurus via the restart menu item, exiting then restarting it the normal way to no avail.
If I minimize it, all the other Lazurus windows minimize as well, but clicking on the Lazurus icon on the taskbar only brings up the main UI, I have to click on each individual window (Message, Object Inspector, etc.) in the taskbar to bring them back up.
Thanks