I work at Linden Lab, the creators of Second Life.
Our client application doesn't work well with Better Touch Tool's window snapping. On dragging the application window, the snapping labels rapidly flash off and on. Or they don't appear at all until dragging the window around for a little while.
Is there any known behavior that commonly causes this type of problem? I'd love to see if we can fix it. Since it's an outlying behavior, I wouldn't be surprised if it points to an inefficient or otherwise undesirable application behavior we'd want to fix for other reasons.
If others want to see the behavior, it's sufficient to download the Second Life client and try it from the log in screen. You don't need to create an account and log in.
If useful for reference, we do publish the client as open source.