When attempting to edit Help:User contributions, even if I just put a space at the end of a sentence I get the error:
Multiple translation unit markers for one translation unit. Translation unit text: '''User contributions pages''' list the edits that a particular user has made. Checking your contributions is useful to refresh your memory about which pages you have worked on (and to easily access these again), but can also be used to find out whether there have been any subsequent edits (see below).
No matter what I change it always points to the line of text "User contributions page..." (the first text on the page). Evidently there are no translation errors, because I was able to make the same null-like edit in the old wikitext editor and with VisualEditor.