I saw a couple of cars like this when I was looking. For some reason it was often on the passenger side. I was told by a well known dealer it could indicate issues with the ash behind the panel holding water, which would result in severe structural issues if not treated. Needless to say I did not buy a car with this issue, not did I buy from that dealer. He might have been giving me a line of course, but in 40 years of mucking about with old cars I have never known bubbling paint to signify anything other than trouble.
