Mount farming in Icecrown - weird stuff with raid

I ran one guy through Icecrown up until the Lich King. I then ran a bunch of alts in (no mount of course). This worked as expected. I extended the raid lock on the main. Later in the week after the reset, I checked my main and it said he had defeated all bosses. It also showed that there was no lock on the raid. Didn’t make sense, so I took him into Icecrown and it showed nothing defeated. I ran him up until the Lich King again, left the instance, and created the group for my first alt.

I went to my first alt and it said he had defeated all bosses. I left the group, took him into Ice Crown, and it said all 12 were available. I left, created the group again on the main, added the alt, took the alt back in and it said all 12 defeated. What am I doing wrong here? The whole point is on a weekly basis run the Lich King on my alts to try to get that mount. Even though 50-60 characters run through the raid fairly quickly, it takes a lot more time for each one.