[cesaref]

I think the point is that the API doesn't specify that the returned integers are positive, or are monotonically increasing, then it's fine for the service to return any unique integer.

If a client application makes an assumption about this, then their engineers will accept this as being their bad and will fix it.

I'd defend this as being pragmatic - minimising disruption to clients instead of the more 'correct' solution of changing the API. I'm hoping that they managed to roll out the new API update alongside the old one and avoid a 'big bang' API change with this. Sometimes this isn't possible, but it's great when that works out.

[CodesInChaos]

I'm far more likely to assume that an integer-id I get from an API is non-negative or even positive than to assume that they're always smaller than 2^31. And I'd be far more likely to blame the API provider for violating the former assumption.

[NetMageSCW]

That sounds like a you problem.