My biggest bubble yet / Bubble Theory

Yesterday I had planned for a post work ride locally to my work. My bike had been left in the car all day but the windows had been down. I opened my boot and to my shock saw my biggest bubble yet! Not sure if the cause was related to a previous self sealing puncture or the heat. Not having a spare tread I figured I would try putting in a tube so I could still do my ride. I deflated the wheel and the bubble held shape. I'm now of belief that the bubble was caused by a previous self repaired puncture, air has slipped into the layers of the tyre and then sealing the inner layer. With a Stanley knife I made a small hole in the outside of the tyre to release the pocket of air. I then inflated the tyre without a problem and was able to enjoy my 18km ride without a problem. Didn't take it easy on the wheel either. The tread was still stretched from the bubble and obviously being held in shape by the inner layer. I will be discarding the tread but was worth the test. I thought I should share this experience and I'm keen to hear other stories and/or knowledge.