CapsLock occasionally behaving as ControlLock

I'm using caps2esc with the suggested setup. I'm running Arch Linux. I have Option "XkbOptions" "ctrl:nocaps,shift:both_capslock" in my /etc/X11/xorg.conf.d/00-keyboard.conf.

Occasionally, and I haven't been able to pinpoint the conditions, CapsLock stops working as either Control or Esc, and starts acting as a sort of "Control Lock", where every other key I press behaves as if it had been pressed along with Control. Switching to a virtual console and then back into X fixes it, but it becomes distracting after a while.

Any suggestion about how I could debug this?