User blog comment:DaNASCAT/Technical Update: October 24, 2016/@comment-4970747-20161024220836/@comment-24473195-20161025105333

"Any word on when the pipe trick in gallery captions will start working again?"

Pre save transform (PST) is the thing that automagically changes the pipe trick into the relevant wikitext. This doesn't work consistently in most tag functions due to the order in which content is parsed. That's one of the reasons why someone misguidedly decided to invent the   parser function, which changes the priority and brings with it a whole range of other bugs.

Perhaps the tag parser function made you think that it worked at some point.