Hydrogen Balloon Fail

I was doing a demo show yesterday, and when my helper attempted to detonate a balloon containing hydrogen and oxygen gas with a lit candle on a stick, the ballon simply popped rather than detonating.  This has happened a handful of time, typically with pure hydrogen in the balloons rather than a hydrogen-oxygen mix.  What I think is happening is that when the candle flame approaches the balloon too slowly, its heat weakens the balloon and causes it to fail.  The gases are then released in such a way that they do not detonate in contact with the frame.