The imagemap plug-in creates a TOPLEVEL window while most other GIMP dialogs are of type DIALOG and I think this is correct. Any WM that thinks that dialog windows shouldn't have minimise and maximize buttons is probably on crack.
I've always thought the same about metacity which is one of these.
Please file it against metacity.But don't hope for fix because Havoc won't allow to change this *#$! behaviour.
Tom Mraz