For example: when pressing capslock the OS pops up a small text message in the lower-right corner saying "CAPS LOCK:ON" and the Arma window starts to blink like it would switch to desktop and back.
This applies to all buttons that have on-screen visual feedback, like num lock, capslock, volume, brightness, wifi, cooling profiles..etc
After the first occurrence the issue does not repeat until alt-tabing to the desktop and back. Then it occurs once more as described above.