Chat overflow on top is still present in version b10 when in slots and having the global chat window open there might be 1 or 2 messages sticking out on top. The side part is sometimes also bugged if too many messages. It cuts of the bottom (overflow:hidden) and sometimes the very last message is not show in case of long messages.

I have the same issue, also when clicking up or down arrow it goes all the way. There is no way to see messages in between. It would be nice to see a date for message posted. This way you have a reference when that person was last "seen".