The Intro notes that "This hypothesis has been recently confirmed in the ant Lasius niger infected with the fungal pathogen Metarhizium brunneum, which induced behavioral changes ..." So it looks like this behaviour might be selected for.
Varroa is really nasty. Sometimes the mite causes colony collapse via death by a thousand cuts, sometimes it's like a nuclear bomb went off and sometimes the bees don't even notice (rare).
I've skimmed the paper but it looks good so far. University of Sassari off of Sardinia produces some very pretty and well researched stuff it seems.