Wasn't this supposed to be fixed ?
I'm on Lazarus 1.6.2, Linux, gtk2 widgetset and it still happens.
On the video you clearly see that the vertical scrollbar is shown then then the horizontal then the vertical and so on... Like if the issue was related to the right bottom corner or something. FInally we're forced to kill Laz by hand...
See the bug here:
http://sendvid.com/jukmamlt.
TBH I don't know how to reproduce it for sure at 100%.