Why is `openin_any = p` restricting access to packages in TEXMFDIST?

[Karl Berry]

    Is there some way I can get the updated version with tlmgr to test
    if it's working now? 

No. Sorry.

    Not sure how quickly commits from SVN make it
    into anything downloadable through tlmgr.

There won't be new binaries for native TL until TL 2021 (April/May-ish,
most likely.)  This fix might make it into distro binaries earlier, but
I have no control or specific knowledge about that.

I'm glad DavidC provided a workaround for now. Thanks David.
(Even further ... maybe xparse could be changed, somehow, until the next
release is out, so as not to fail here?)

Best,
Karl

P.S. It is correct that people "should" include you on CC's, and it's
also good that you're checking the archives for replies, because
sometimes people don't :(. It is perfectly fine not to be subscribed to
post; this is the case for nearly all tug (and gnu, as it happens) lists.