Yes ... that's the obvious loop-hole in the process (system) Karl has described.
Unless, that is, there is some sort of cleverness (data logging) inherent in the swipe-card technology being used.
Either that, or how about adding PIR (motion detection) and a web-cam?
I suppose that the ideal "technical solution" might be to have RFID tags fixed (hidden inside, screwed - or glued - on, welded even) onto every piece of kit and have a detector (induction loop?) at the MEL door(s) to enable automatic logging in and out!
Not that I'm really into spying on folk (staff), of course - there's probably far too much of that going on already - but if they keep "forgetting" to make log-book entries (or whatever), how else are you going to enforce a bit of discipline?
... which just needs to be swiped over a black pad which is located in each ward ...
There's the weak link, right there. How about having the "black pad" on the counter in the MEL?