CTRL on external keyboard

I'm using PocketCloud for Android on my Toshiba Thrive tablet to connect to a VNC server on Linux. Most things work fine, but one essential detail is causing troubles: the CTRL key on my external keyboard does not work properly (the same problem appears both with a standard USB-keyboard and a "Logitech Tablet Keyboard" connected via BlueTooth).

If I want to send e.g. CTRL+A, I cannot do it simply by pressing those keys, but I can press CTRL+A (or anything), A, CTRL. Pressing CTRL+anything does not seem to send any keyboard event, but all subsequent keypresses will be with CTRL enabled, until next time I press CTRL.

I'm using programs that rely heavily on CTRL. Using the on-screen CTRL is not an option. I'm currently using the free version of PocketCloud, but if I can solve this problem, I will buy the Pro version.