Hmmm...don't remember where I got that information from, so I could well be remembering wrong.

I do see that pspdfkit folk are active in the pdfium bug tracker, for example:

https://bugs.chromium.org/p/pdfium/issues/detail?id=641

That sounds like a production problem, but it could just as well be them trying it out.

It's certainly quite plausible that they compare their behavior with other engines, and then file bugs on those other engines if they find them.