When he was a hatchling/under 600g I used paper towels as a substrate he did the same thing after every poop- bang his head on the lid/thrash around the enclosure and I would subsequently throw everything out, wash the tub, and he would ball back up under his hide as usual.
I recently tried out Reptibark as a new substrate however (eventually switching to an acrylic tank for display in the future) and all has been going well until 2 days ago- it's been the first time he's pooped/peed in 2 weeks, I tried to spot clean the place where he pooped (under the hide) but he's avoiding that spot like the plague and is trying to escape from the enclosure again.
Here's a picture of the setup: The hide is part of an old architecture assignment mockup I found and modified to fit in the tub. It's extra long and covers both the cool side (79 deg) and warm side (93) and the humidity seems to be right too.
http://i.imgur.com/irGwNnv.jpg
What am I doing wrong.. is spot cleaning maybe not enough? Do I have to throw out all the substrate every time he poops if I'm going to be using bark as substrate