But http://code.google.com/p/android/issues/detail?id=2229 mentions that it got fixed not in Android, but in the CalDav App - which makes me think that possibly it would have to be fixed in DavDroid (which is a sync adapter, too), too.
OK, it’s clear now, thanks.
(What is the “CalDav App”? There are several ones.) Assuming you mean CalDav-Sync, I guess that it handles event instances itself instead of relying on the Android calendar provider – this is a different design approach and can’t be done with DAVdroid. DAVdroid relies on the Android API for recurring events, and when the Android API is bugged, the bug has to be fixed there. Also, CalDav-Sync isn’t open-source (yet? although this has been promised), so I think it doesn’t provide any benefit to know what CalDav-Sync is able to do.