MJ Mod - sucks after cleaning?

[SDguy]

Why is my MaxiJet 1200 mod being such a problem after cleaning it? It will run fine, then all of a sudden the piece that has the white propeller on it will jump forward (away from the pump, and the magnet) and rattle like all hell. Then pop back into place and be fine. What's that about?

[SDguy]

OK, next question. On this mod (AlgaeFree brand) why do they make the shaft long enough so that the piece with the propeller on it can completely separate from the magnet? I'm assuming there is a reason for this...