As Vavoom said, those buttons are a function of the WM. You might check out Tk::WM, specifically, the $toplevel->frame() function.

Also, as a hack to work around it (if you can't be sure which WM it will be), you could try setting a handler for the WM_RESIZE or WM_MINIMIZE/WM_MAXIMIZE (and no, I'm not sure that those are actual messages ;-) using $toplevel->protocol(?name?,?callback?), or even just try disallowing resize completely with $toplevel->resizable(0,0).

Just some suggestions to try. I don't know if any will work. Hope it helps, though.

bbfu
Seasons don't fear The Reaper.
Nor do the wind, the sun, and the rain.
We can be like they are.