My iMac 8.1 is partitioned into separate accounts for wife and kids.

My iMac 8.1 is partitioned into separate accounts for wife and kids. If I power up / use it / put it into Sleep mode, that works. If my wife's account has been used and she has logged out and I try this sequence in my account, then the computer goes into Sleep mode for a few seconds before popping out again. Repeatedly hitting Sleep doesn't help. It sounds like a software issue on her partition carrying over after she has logged off. Why?