As far as I'm aware they're also banned on a fair number of other carriers... when in doubt I'd say anything that is smoking ( or APPEARS to be smoking) is probably not a good idea... if you're going to the toilet to do it and you admit that it *might* set off the detector than maybe err on the side of caution and not use it... otherwise one day you might get an extremely angry telling off from a crew member with a fire extinguisher in hand! :P
I'd imagine also that this would cause more problems on carriers where most of the passengers might not speak English/French/commong language as once they see, they do- and they might not understand the difference as you say.
Any EK crew care to comment? Anything in your manuals about this?