Anybody else's Hibernate and Sleep button disappear sometimes?

[Silpheed2K]

Sometimes when I hit the shutdown option... I notice my Hibernate and Sleep button are gone... just the other 3 buttons are there.
I wonder if it's certain apps I'm running (that can't be allowed to go into Hibernate) or if it just happens at random for no reason.
Has anybody else had this problem? and what is causing this?

[Silpheed2K]

This is what my shutdown window look like sometimes (username blurred out)


Hibernate and Sleep work fine; However, the buttons just disappear from time to time and I don't know why. Does anybody have an idea of what's going on with this?