An important first question to ask is what internet browser do you use?
Regardless I will replicate the situation and see what I find.
EDIT: I replicated the situation by having 2 "burrowed" Devourers on the field and then playing Pandemonium (unupgraded). Nothing odd happened. I could end my turn. I could "unburrow" them and I could play cards.
I seriously think it has to do with your browser, mainly issues with using Opera. I hope I've helped.
I tried several more times, but I always suffer this problem.
My test was.. (in Top 50)
1) 2 borrowed devourers on my field, no enemy creature
2) 5 borrowed devourers on my field, no enemy creature
3) 7 borrowed devourers on my field, one immortalized (by Quintessence) elite otyush
4) and more which I can't remember ..
Pandemonium works well if there is effective creature.
I tried again with clear internet temporary files in chrome, but nothing changed.
Is there anybody who can check this problem for me? ioi