I'm using Windows 10 (Build 10586.14) Enterprise x64 and the latest version of 64-bit TightVNC as of 11/26/2015.
In Windows 10, if you have dual displays, each one can have its own DPI settings. I have two monitors, one set at 100% and the other set at 125%.
VNC works just fine on the 125% monitor. When I mouse over to the other monitor (the one set at 100%), where the cursor is actually at and where the cursor appears to be to me are different. It's off just enough to make the second monitor unusable. When I bring the cusor back to the first monitor, I can still use the first monitor just fine.
To reproduce:
"Mouse Cursor -> Let remote server deal with cursor" and "Local Cursor Shape -> Do not show" viewer options can be used as workaround
This is connection specific. Can it be default option for all connections?