Never heard of this happening:
I made little "hooks", using 2 brass elbows, on the end of two of my silicone tubes. They hang on the edge of the MLT or BK to allow water or wort to flow in.
I pumped half my sparge water into the MLT and started recirculating. My son looked into the HLT a little later and asked why it had "layers" in it. The tubing to the HLT had siphoned some wort back through the pump, into the HLT.
Not a big deal, I just pumped it back into the MLT with the rest of the sparge, and I had to clean the HLT.
I learned to close the HLT valve when I'm not pumping water.