It seems to be more complicated than just "PAR wraps your script in a subroutine, and that's the source of the problem." If that were the case, then any program that uses the cache/closure idea should cause the warnings.

The toy script in the OP generates the warnings, but another script where I did something similar did not.

So I'll have to work up an example along the lines of the toy script, but doesn't generate the warnings, and show the minimum tweak that does generate the warnings. (Or some kind soul can chime in with a satisfying explanation.)