It happens to me that, when I have tabbing on (even if there's only one conversation window), the scroll bar gets fucked up. If I try to scroll up, after one second or so, the bar returns to the bottom of the conv, no matter what. This happens both when I scroll holding the scroll bar, clicking the up arrows or scrolling with the mouse. So I can't read stuff that have been said earlier . When I turn off tabbed conv, this doesn't happen.

This is actually a bug with MSN Messenger and the way the conversation window is designed. In order to read the conversation you need to click on the sent/recieved text and use your arrows to scroll.