All move requests send by an application, for example using gtk_window_move if GTK is used are ignored as long as the window is maximized or fullscreen.

In my opinion it would be more correct behavior to switch to normal mode and move the window in this case.

This does not seem like a problem at first, as it does not really make sense to move a maximized window at all. Unfortunately in a multi-monitor (multi-head) setup one might intend to move maximized windows from one monitor to another, from within an application.