My best guess is after borrowing and dumping over 600K between May 31 and June 15th, that now those behind the short selling are covering off...and adding what they can.  

I would imagine its effective too, after seeing the PPS drop all the way from $2+ to a low of $1.23 I have little doubt there are some players sick of the roller coaster who are more than happy to walk away....happy to get $1.30, $1.40...$1.50 or whatever, happy they didn't have to sell at $1.23 or less.