In other news - water is wet!!!
Happens from time to time. Some people deny it, and make excuses that they're after algae on dead tips and whatnot. Which may be true, but I've also seen them go after nothing but healthy acros before.
Interestingly enough on a casually observational basis, I've only ever seen the large males do this. Females have always been well behaved in this respect, as have juvi males.
I have banished them from my display, save one female my daughter insisted upon getting. Kids, right?