I played the demo as Austria and there was a revolt in Flanders. Rebels declared independence while my troops were still on the way to defeat them. When my troops finally arrived they conquered all revolting provinces and destroyed their armies. I now have 100% was score but I still can't annex them, because apparently annexation requires over 100% warscore. This seems bit odd to me, because I'm forced to recognize their independence as OPM even when I defeated them in their independence war.