I have the same problem with bed pillows. I ended up opening the seam by three inches, then safety pinning shut for the wash. Air escapes that way. It's a pain to sew the seam back up. Probably too much work for a comforter.

I have a GE w/agitator ( GTW845CSNWS ) It's 5 cu ft and yes, it's on Bulky/Comforter setting. And yes I have an Auto Soak setting and used it. This didn't just start with this washer, it's always been a problem with "puffy" items. I was just hoping someone had a technique that worked. If it was a smaller item, I would have put it on the bottom.

Try filling the washer, getting the comforter as wet as you can, punching it down, turning it over & then drain the washer & let it spin. The spin cycle helps to expel the trapped air. Now that you've 'rinsed' the comforter, back up and fill with water & proceed with the wash.

Humm, that might work. Thanks

ci_lanteo's suggestion is good because you have a top loader.