I've noticed there are a few issues like this discussed related to bpatchers but I haven't seen anything like this specifically.
Basically I have some message boxes inside bpatchers and I have some objects ontop of the bpatchers. The bpatchers are brought to front and display correctly until the patcher is made fullscreen. Then the message boxes inside the bpatchers draw ontop (front). Message boxes normally draw correctly unless they are in the bpatchers.
This usage might seem a little obscure but the behaviour is still not what is expected. I can use the refresh message after some delay. This is not ideal since I can't be sure when the fullscreen redrawing has finished, 500ms seems safe but untidy since the message boxes display briefly before being drawn correctly.
The actual usage employs a custom object (which I first thought was at fault) and I'm resizing this on going fullscreen to obscure the message boxes. But as the example shows it happens with built in objects too. (2d slider in this case.)
Max/MSP 4.5.7 OSX10.3.9