Why some applications sometimes become not "minimizable" on OS X?

"I am not sure myself but a quick Google search reveals some interesting theories:

From MacRumors:

For some reason the OS seems to get
disconnected from the Dock and
disables the minimization. I haven't
found a cause yet but I usually find
that opening
/Applications/Utilities/Terminal.app
and running: Code:

killall -HUP Dock

fixes it. The only downside is that
all windows which are currently having
issues will not suddenly start working
but all new windows will behave
properly."