Yeah this pushes developers of the platform between a rock and a hard place.

It's ok to keep backwards compatibility, but the API needs to also move forward and get the bugs ironed out. The worse case is when developers start to rely on the bugs for their workarounds (yes, please, do test your API before releasing)

Maybe shims are the way to go. Instead of keeping old functionality around you make a shim that only talks to the new API. And that will serve as a guide (because if you're taking functionality out that's usually not good). I've seen a couple of cases where the deprecated API was much more straight forward and easy to use than the new one. Not good.