Rebels broke Austria-Hungary.
From what I gathered there was a mix of Austrian Nationalists and Anarcho-Liberals. When the government fell, Austria broke away, but promptly triggers the decision making KUK. So then Austria-Hungary is formed there, and the former Austria-Hungary becomes Austria. Back and forth, every day.
Has this been encountered in the past and/or fixed in the new patch? I still have the saves. If nobody has been aware of this, I will post a bug report. The main reason I have not done so yet is because this is a 1.2 game that I am finishing before adding the latest patch.