It seems that at some point our windows were stained with an oil based stain. Since then they have been painted with acrylic, including the lovely dark blue (Kosciusko) in November.
Oil and water don't mix, and so just last week we noticed that the paint was bubbling badly in places.
It seems the acrylic paint doesn't like the oil stain which is embedded in the wood and is trying desperately to get away.
The painter happily returned it fixed the existing problem, and gave us paint to fix any more bubble that might appear ("which will happen").
Given how bad the windows were before, even bubbly paint is better than exposed to the elements rotted wood carnage, but I think I can "scrape, sand, paint, wait, paint again" as good as anyone else.
While out there watching him paint and looking after the distressed dog ("there is an OLD MAN in my backyard!") I noticed the fence out the back is starting to flake. The bits I didn't sand off properly have popped off to leave black spots. Yay. Guess what I'm doing Sunday?