When UAC prompt is opened with secure desktop disabled (HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\PromptOnSecureDesktop = 0) and TightVNC server is running under regular user, the session turns into view only mode. The view only mode persists even if the UAC dialog is locally closed and the TightVNC server needs to be restarted to function normally.
This seems to be regression because it worked in the past (in Win 7). I am not sure which update breaks this, if TightVNC update or Windows update. I am encountering this with Windows 7 Pro 32 bit (server) and Windows 8 Pro 32 bit (client). But I think this happen with other combinations as well. I am using TightVNC 2.7.10 on both server / client. I tried w/wo mirror driver, all the same.
This is very annoying, because you can easily lost your remote session by one bad click.