You are wrong about end of month margin calls.
There is no such thing!
Your margin/buying power is calculated each day based upon the closing bid price and margin calls are made each day the following morning if your buying power falls below what your margin debt is.
Trying to blame the share price drops on margin calls or short selling simply won't work!
The only thing that does work is when there are more willing buyers than willing sellers__and right now there are way more willing sellers out there.
But don't worry soon The Rock will come here and once again post a very nice warm and fussy post which should reduce your angst!