4.3.2 describes what a UA MUST and should do "when track constraints change".

At the very least, this should be referred from the applyConstraints() method description.

The said description should be following a step-by-step algorithm, and incorporate some of the conformance requirements currently described in section "The model: sources, sinks, constraints, and states" (e.g. the dispatching of an overconstrained event).

The same 4.3.2 says "Similarly, if the sourceType changes, then the user agent should perform the same actions to re-evaluate the constraints of each track affected by that source change."

It's not clear whether it is meant to be a SHOULD rather than a should, or even maybe a MUST; it's not clear to me what could make a sourceType change in the first place.