I would second what @heathlindner25 suggested. Go back to your cleaning location and look for a little piece of clear tubing(I think it is called cover rubber). Search for Jebao wavemaker replacement parts and you should see them. If it isn't missing then it will at least show you assemble and disassembly so maybe you will see a part. Either that or you don't have the top rubber piece properly set into the cover.
I have a RW 4 and 8 and don't have this problem. Remove from tank, remove rubber gourmets on the sides, twist and turn housing to pull apart, remove rubber cover on ceramic shaft, remove shaft, and clean. Make sure you don't loose the bottom one although it will usually stay in place. I'm sure you already know all this but that is more or less what I do. The tiny rubber cover piece holds the shaft and impeller stationary once everything is put back together.
Good luck.