My black & white percs have started doing the same thing. 
 
I have little holes in the sand, about 3-4 inches wide, where they've tried to clean & dig all the way to the glass.  As a result I'm having sand storms whenever they decide to clean their sandpits. 
 
Nice to see they're comfortable enough to feel they can re-aquascape but a PITA for sure! 
 
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