Ok, I looked at the tab three of AP options and it allows to set a default bank code or use the last bank code used but that's not my issue.
My issue is that bank code H has a default form code H but that is not being used when you bring up bank code H, instead form code A comes up. I don't have access to the client right now but I'm going to try changing the default form code to see if that has any effect. I haven't found where the form code information is held. it's not in GL_bank.