"Known problems" says "Probably many more, please report them." without a link where to report them. Please see https://phabricator.wikimedia.org/T111105 and https://phabricator.wikimedia.org/T111103 for existing bugs.
Topic on Extension talk:PGFTikZ
I was assuming the talk page would a natural place to report bugs. Is there a better place?
Thanks for reporting the phabricator bugs, I'll look into them (I had not ported my account there).
Wherever you'd like to manage bugs, making it explicit is welcome. :) Regarding creating a Phabricator account, it's just a few clicks and no new password, see https://www.mediawiki.org/wiki/Phabricator/Help#Creating_your_account_and_notifications - Thanks!