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There might be some cavitation at the impeller, but I doubt it. The cavitation we are talking about (imprecise choice of words) is happening in the pickup tube. The theory being it sucks some air/froth as a result of braking/turning in. But the shape (and according to me the bulbous mid-section) prevents it from quickly re-establishing good flow to the pump.
Imagine sucking fluid through a straight straw... if the straw loses contact with the fluid, you will suck air, but flow will resume immediately as the straw is immersed again. But consider a straw with a big bulb in the middle... it takes longer to re-establish flow because the bulb is full of air now and has to be drained--its pressure must fall sufficiently below ambient to suck up the oil... and a larger volume of gas takes longer... especially since the pump impeller is designed for low-volume hi-pressure operation in fluid, not sucking on air. Just a theory...
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