I noticed that, in one of the third-party databases I have installed
on my server, one foreign key constraint could not be implemented.
(The key columns are of incompatible types.) In previous upgrades I
had seen a warning concerning this constraint, and had passed this
information along to the people who maintain this database, but they
ignored it. Now the warnings have turned into an error, and the
constraint isn't being implemented.
So this is an issue I've been aware of for a long time (more than two
years, in fact), and if I'd been responsible for maintaining the
database, I would have fixed it long ago.
Maybe I'm overly optimistic, but I get the impression that, if you
pay attention to warnings and fix your problems in a timely manner,
you're unlikely to be blindsided when the rules get tightened up in
subsequent releases.