Strange; well, as I said, my 110 is very tempermental in that way...sometimes it will start up after a water change that may take 20 or so minutes, while other times it makes the "choking" noise, requiring me to pour water in to prime it...
I only had problems before I knew that the impeller needed to be pulled out every so often and cleaned inside of the motor with a Q tip or small brush. I now do that every 4 months and all start as long as there is an inch of water or more in the impeller chamber. The ac 50 I have is about 7 years old and still going strong ( I probally shoulnt have said that) How ever I agree with you that all these hob filters should have the impeller in the pick up tube in the tank side so you dont have to refill the filter after a water change.