As discussed on #979, there is currently a bug in persistent-postgresql that causes migrations to fail when there is more than one constraint on a single column.

This is an issue when you have e.g. a foreign key to a field and a compound foreign key with that same field included as shown in #979 (comment).

I've already written a failing test on another branch, and @robbassi has an incoming PR to fix this issue, so this is just for documentation purposes.