Xander found out that sometimes, some Dependency "change" callbacks are not invoked.
For instance, assuming the following scenario with three components A,B,C:
1. B adapts A and in it’s init adds an instance bound required dependency to C.
2. Now someone modifies the service properties of A
3. As a result of that C (which somehow has a required dependency to something requiring A) becomes unavailable
4. B becomes unregistered because it’s dependency to C is no longer satisfied
5. Because there’s a check on ds.isRegistered() in the change method in _modifiedService B will never get notified of the new service properties
in step 5, B is not notified in B.changed(A) because B is in the "waiting for required (instantiated)" state. So, fixing this problem consists in calling ds.isInstantiated() instead of ds.isRegistered() method in ServiceDependencyImpl.doModified().
Other kind of dependencies might also have the same kind of problem. For example: BundleDependencyImpl.