There are many examples of unclosed pages tags on at least English and Multilingual Wikisource, suggesting that they did trigger the ProofreadPage extension behavior at some earlier time and there has been a regression.

Steps to reproduce:

1. Create a page with the content:

<pages index="example.djvu" from=1 to=10>

Expected results:
The pages from 1 to 10 of example.djvu appear, or an error stating that example.djvu doesn't exist

Actual results:
The text

<pages index="example.djvu" from=1 to=10>

appears.