[gentoo-user] [OT]: "Reset" of USB when switching to console and back to X?

Hi,

I have attached an old keyboard (PS/2-connector) via an
USB-PS/2-adaptor to my PC.

When typing too fast (...) the three LEDs of the keyboard flashes 
and everything typed then is typed as if the CTRL-Key constantly
locked (I am using the X-window-system with openbox as windowmanager.
There is no session management.)

It is possible to revert back to normal when I switch
from X-windows to the Linux console (CTRL-ALT-F1) and back
to X (CTRL-ALT-F7).

My question is: 
What part (PC? Adapator? Keyboard?) gets out of sync here is 
"resetted" (somehow), while switching between console and
X-windows?

How can I reset the behaviour without switching? How can I
prevent the behaviour completly?

Best regards,
mcc