[Synergy v1.4.17] Modifier keys (Shift, Ctrl, Alt, Win/Cmd) repeating instead of being held down (Win8.1Pro server to MacOSX 10.9.2 client)

I'm using Synergy v1.4.17 on the server (Windows 8.1 Pro on Alienware 17) with the client (Mac OS X 10.9.2 Mavericks on Mac mini Server, Mid 2011), connected with ethernet cable.

Whenever the Mac is active and I try to hold any of the modifier keys, OS X will report the key as being rapidly repeated rather than being held down.

This makes existing single-modifier key combinations unreliable and all multi-modifier key combinations completely unusable (the OS will only detect the most recent modifier key).