I haven't reproduced this yet (I'd need to code an app to try it) but looking at the code I think there's a missing check.

When XAccountManager hooks [addOnAccountsUpdatedListener](http://developer.android.com/reference/android/accounts/AccountManager.html#addOnAccountsUpdatedListener%28android.accounts.OnAccountsUpdateListener, android.os.Handler, boolean%29), it doesn't prevent the listener to be registered as it's merely overriding the result to null after the call, which it already was the original result (void).
If an app registers a listener it will still receive the accounts changed after that, and if updateImmediately is true then it will receive the current list.

Sorry if this is already covered by the other hooks, but looking at both XPrivacy and the AccountManager code, it doesn't look so.