I have a problem as well with these but not only turning off, but on as well.
It seems the RWS17 wall switch does not like to share the common wire with another unit in the same gang box. When I put two in the same box next to each other, I get random behavior. Turning on one unit will cause the other to go on, usually a few seconds later or turning one off cause the other to go on. It's totally random.
I turned on off and the other works well, then I turned it back on, and pulled it out of the gang (hanging out of the box, looks classy) and the separation seemed to help. I havn't troubleshot it all the way, but it seems like the house wires might be to blame on the common side of the wiring.
I ordered a phase coupler/repeater, once that's in, I'll update here when I get it resolved. If anyone has the same problem, or any ideas, I'd love to hear them!! Thanks!