My take on it too Si. We have burst many bubbles, hence bubbles burst is correct.
If we had only burst one bubble, then it would have been bubble's burst.
Is this not right? :?
I would have thought that the article would be referring to a single situation of the bubble bursting (singular, but applied metaphorically as a generalisation) hence saying 'bubble's burst!' as an abbrieviated colloquial way for saying 'the bubble has burst!'?
To have it as a plural sounds strange as a colloquial abbrieviation alluding to many bubbles that have burst in one go, as if you were to say something like: 'Oh, the bubbles burst, ay?!' - thinking about all the bubbles that have burst in the past, or maybe: 'Look at all the bubbles that have now burst!'
You surely would have to add something like 'Many' at the front for it to sit right, if this were the case?
'Many Bubbles Burst!'