Ubuntu releases a holding key after a few seconds

[makemonday]

Hi!

I am using Ubuntu in VirtualBox and it works pretty fine, but there is a problem that I am having since I started using it. I use Emacs and therefore, I use a lot of combinations/shortcuts/bindings all the time. The problem is that when I press and hold a key, for instance, CTRL for searching (C-s), if I want to keep looking I just hold it, but in this VirtualMachine after a few seconds the CTRL key is released (without me releasing it) and I finish writing a bunch of 's', in this case. Another simpler example would be, changing windows with Alt+Tab, after a while Alt is released and I end up pressing just Tab in the last window changed. I guess this has something to do with some kind of refreshing of the peripherals or something, but it is really annoying.

Any ideas on how to solve it?

Thanks a lot!