This is a clear example of what happens when you pick at a bit of flaky bog - rust in behind meant the whole repair had to be re- panel beaten and done properly. The resins from the bog hit the steel and cause it to lift- letting moisture in. A good reason to consider laying down an epoxy primer( PPG dp40) prior to bog work - not necessary but would have prevented this from happening. Also the acrylic paint is porous - thus letting in the moisture- don't use acrylics and you will avoid this scenario more easily.....