Ok, so I thought I'd start off my first CK2 in Ireland. I had a du jure claim from the beginning, and pressed it right away. No, I won't be naming names. I am away from my home computer right now, and they all sound like dachmachganachach to me. Anyway, I raised my levies and he raised his. We were about equal. I attacked and was defeated, with both armies nearly annihilated. After that I won a series of small engagements with the tiny levies I was able to raise, and finally I was able to win with an army big enough to lay siege to... to... the province. After I finally crushed the defenders (progressing with 3,4% every 12 days), I got those red occupation bars on the province and the siege... started all over again. This time with MORE defenders than before. Luckily, at that point, my victory score was at 100% and I was able to enforce demands.
BUT... the former independent now became my vassal, and still in charge of the province without me having any say in the matter. He hated my guts, of course, but the funny thing is that the rest of his family - his wife, his kids - and his entire court seemed to love me. Anyway, I couldn't revoke his title because apparently I didn't have any reason to do so, so I had to initiate a plot to do that. The plot succeeded, but Mr. Irish, here, didn't like it one bit and rebelled against me. With 97 men. At this point I raised my personal levy of about 1000, and crushed him. New siege commenced.
And...
I won the siege, but this time no occupying bars, and victory score only at 9%. And the garrison was now twice as big as before. I couldn't enforce peace, and I had to raise more levies to win the new siege. After the new and completely pointless siege, I won, and then their leader - and all his family - and all his court - simply disappeared from the game. Damned shame, because I could have used them all (their opinions of me were unfeasibly high, under the circumstances).
So, is this a bug, or am I missing something about the siege mechanics here?