I think I found a bug for synergy. I have tried it in 1.3.6 and 1.4.2 beta, I also got a user (frankivo) on the synergy IRC channel to verify it.
Steps to reproduce (on a client): 1. Open a text editor 2. Press one of the shift keys and keep it depressed 3. Type: ACTIVE 4. Press the other shift key and release it (while still keeping the other shift depressed) 5. Type: SHIFT Result: ACTIVEshift Expected result: ACTIVESHIFT
So, the shift status gets set to deactivated when any shift key is deactivated without checking for any other keys.
Hope someone can verify this and file a proper bug/issue since new users aren't allowed to do so.