Created attachment 244401 [details]
Test program to show the difference between resizable and non-resizable dialogs

Setting a default size with :default-width and :default-height works properly as long as the dialog is resizable. Once :resizable gets set to FALSE the dialog goes back to its minimum size.

In case that's expected I just find it pretty much surprising and should be documented along with the :resizable property and gtk_window_set_resizable().

Test program attached, runnign three dialogs: the resizable one has the desided size, setting :resize=FALSE in an idle callback shows that the dialog changes its size from the desired default one to the minimum one.