Sometimes the anchor links generated by the Index: page's <pagelist /> for existing Page: namespace pages do not have the expected class attribute and value (class='qualityN prp-pagequality-N') set. In these cases, IndexPage in proofread.py fails, as it relies on this info.
A null edit of the Index page refreshes the status, and the class reappears.
Note: The anchor links generated by an Index: page's <pagelist /> for non-existing Page: namespace pages (pages yet to be created) do seem to all have the expected class attribute and value as any other redlink anchor link would (class='new').
Would be good to:
- understand why this happens (so countermeasures might be taken, at least in pywikibot)
- make IndexPage in pywikibot more robust or give errors when such situation appears (and possibly skip tests)