using rebel lands as buffer zones

[Alexios]

3. It also seems this is more of a problem with certain provences on the Eastern side of the map although I can't remember which ones they are.

In my current campaign as English, I have taken over most if not all of Asia (I saw an opportunity in Scandinavia, but then just kept going). After I had eliminated the GH, I experienced a nasty little surprise, but it wasn't with the rebels. After about a year or two of taking over Volga-Bulgaria and Khazhar, the Turks suddenly re-emerged in those two provinces - 2 stacks in VB and 4 stacks in Khazhar. Not sure why they popped up there, unless perhaps this is where the GH had conquered them earlier on. But nevertheless, it was quite a surprise. I had to quickly shift my armies from my western flank over to the east - and it was right as I was about to launch a major counter-offensive against the Poles!