Hi Neil
I have a Japanese article on red pine which specifically says it's ok to let them become so pot bound that they push up out of the pot some. So I would suggest the either the pot is too big or too much water when it does not need it or the wrong kind of mix or a combination of these. There's no doubt that red pine is very drought tolerant. I water (and feed) mine once for every two times I water a black. 50% sand/gravel (at least) should be part of the mix IMO especially for an older tree. They don't mind a very lean soil mix.