Squeaks, I've flown with a couple of companies that had the same limitaton re floats on the AOC and at one Op we were always over water.
It's a strange one, but I believe that it relates to the CP and if they have a float endorsement or not, remembering that you have to have the endorsement before you can operate with fixed floats. Therefore if the CP doesn't have the endorsement, it wont appear on the AOC.
I also know of one school that did fixed float endorsements, but wouldn't sign the pilots off until they had a HUET!
The AOC bit is just speculation as I had asked once before, but couldn't get an answer.
Glad to hear everyone is okay.