So I just formed Qing after taking the required provinces off of Ming. It was around 100% overextension, quite alot but manageable. But as soon as I formed Qing several of my other provinces became uncored all of a sudden. I didn't lose them but they also weren't cores anymore, so now I'm sitting at 200% overextension (150k rebels already spawned) and now I have to recore provinces that have been mine for 100 years. Was this supposed to happen?