This is on Unity 2D and Bug #780803 is at least tangentially related. Synergyc is connected to server through an ssh tunnel (which I set up according to http://ur1.ca/7g6o9#), with client positioned left of the server.

Steps to reproduce:
1. Bring mouse cursor from server screen to client screen.
2. Press Super on server keyboard.
3. Bring mouse cursor back to server screen.

What happens:
Synergyc dies with a segfault:
segfault at 8b0a75c8 ip 0062fbf2 sp bff05108 error 4 in libstdc++.so.6.0.16[5d8000+d8000]

(Also, pressing Super at step 2 brings up launcher on server, not on client – that’s probably Bug #780803 manifesting on U2D.)