The uniqueness of track IDs?

When setting a remote description containing audio and video tracks with
the same ID, what is the expected behavior?
Is this OK, and you have two tracks with the same ID, or should it be
rejected?

I've previously realized IDs aren't unique in the sense that you can add,
remove, and then add again with the same ID and end up with multiple track
or stream objects with the same ID, but I had thought that amongst streams
and tracks currently in-use the IDs would be unique.

Should the audio and video track IDs be considered separate domains? Or
should I simply make no assumptions about the uniqueness of track IDs?

I'm investigating a crash related to audio and video having the same ID.