(previously discussed with @ssastry who figured out that it was caused by srcTagName)

If you have wikitext like <FONT color="blue">foo bar</FONT>, Parsoid will store "srcTagName":"FONT" in the data-parsoid so that it roundtrips correctly.

However, you modify the tag name in the Parsoid HTML, e.g. <span style="...">foo bar</span>, but leave the data-parsoid alone, then when converting it back to wikitext, Parsoid will use the value in srcTagName and then overwrite the new tag name with the old one.

This is a bit of an edge case but one my bot is running into when fixing obsolete-tag lint errors. I think the simple fix would be to check that the value in srcTagName still matches the node name before using it.