Using virtualenv changes cutoff from 128 to 260KB

Using Python from a virtualenv changes the cutoff point from 128KB to
260KB. Maybe my system Python had some site packages installed that
affected this?
Running the for loop 2X changes the results

There is no longer a dropoff at 128KB.

This was run without a virtualenv.
Using "del mystr" fixes the problem

I thought I tried that already
Using a dict w/ del statements gives similar results
Now running 2X gives expected results
Revert "Now running 2X gives expected results"

This reverts commit b9e7de6dddf1785dc1010a76377b7a5f365ab36c.