Your describe window is probably configured as a “stay on top”,
which means it stays on top of Toad’s main form and can be dragged
anywhere on your screen (or to another monitor). Those other windows (alter
table, analyze table, etc) are MDI Children – which means they have to
stay inside Toad’s main form.
So, either move the describe window out of the way, close it, or uncheck the
“stay on top” checkbox on it. If you uncheck “stay on
top”, then the describe window will become a MDI Child, and will go into
Toad’s main window like the others.