Following the escape of some bees into my room - I decided it was a good idea to work out how they were getting out. I ended up using lots of heavy steel ball bearings - each with a smaller circumference than that of the bees. I gave the hive a good extended vigorous shaking to work out where the ball bearings were able to work into gaps in the foam inner sections. I then modified the plan drawings so that the glue better protected against this happening. After re-sampling the hive I haven't had an issue since.