> did you try enabling the "Elevated" mode in the client (should be > selectable at the bottom of the main window)?
Nope, because it's not a Windows machine, both machines are Linux. I did however get a chance to do a little debugging, although I wasn't about to learn much. I discovered that when synergy owns the selection, it seems to always have the property member of the selectnotify event set to None, while other applications do not. However, I also notice that after that first successful paste into st, st no longer receives selectnotify events. That's about as much as I learned. I'll see if I can spend some time on it tomorrow.