Mmm I'm curious on that one as well. I've had anemones in trickle filters and main tank with sump and they still always deflate. It's their way of expelling "used" water which is what they're full of.
when i do water changes in my tank without the sump, anywhere from 1-3 days after my rose tends to shrink looking almost dead sometimes, and always revives eventually. However on the wet dry, they usually never shrink. Coincidence? I think not