It seems T136401 has side effects because
<nowiki><span class="error"></nowiki>
is now parsed and makes things red
Found by a edit https://de.wikipedia.org/w/index.php?title=Hilfe:Vorlagenprogrammierung&diff=159245317&oldid=157586434 on dewiki
See the red text after "z. B." in the old version: https://de.wikipedia.org/w/index.php?title=Hilfe:Vorlagenprogrammierung&oldid=157586434#Funktion_iferror