Perhaps it's OTC BB rules.

When the pps is below .50, then the minimum size for the offer both bid and ask is 5,000 shares.

So if the price was below .50, then they would EACH have to offer a minumum of 5,000 shares at a time.

Now if the pps is over .50, they can drop the amount of shares they want to sell at a time is 2,500.

Think of how many extra shares they could lose if the pps had to go from .37 to .4999 on the way up since they could not offer less than 5,000 at a time.

now multiply that times the number of mms trading PTSC (amongst themselves, for the most part to keep the pps down... but that's another theory...) and you can see why .50 is a support, for now, anyway.