Now that I'm at home, I thought I'd show you why in particular I'm not a fan of tissue paper touching cels...
http://home.insight.rr.com/gabrielstuff/tissue.jpg
Now, I don't know if this is the exact kind of paper you are using, MacKettric...its kind of smooth and shiny on one side and a matte, slightly rougher surface on the other side. The shiny side seems fairly stick-proof - at least I haven't seen it stuck to anything yet. The other side...not so much. Having just spent the last two weeks picking out little tissue paper fragments out of hanken linework, its fresh on my mind. ;)
I suppose tho, if the fronts of the cels have no paint on them, it would be ok. Doesn't matter if the back sticks, since ya can't see it.
And out of curiosity, what was the opinion you heard on bags? Was it the fumes build-up thing, or was it something else?