https://en.wikipedia.org/w/index.php?title=Special:Contributions&target=Asdklf; exists and shows an editing history.

However, clicking on the user name on that page takes me to:

https://en.wikipedia.org/wiki/User:Asdklf;

which (at the time of writing) displays a page for an unregistered account, "User:Asdklf" (note absence of semi-colon)

This all occurs in both Firefox and Edge, both fully updated, under Windows 10.

Attempting to edit via:

https://en.wikipedia.org/w/index.php?title=User:Asdklf;&action=edit

in Firefox, in source editing mode, shows the expected page markup, but if a change is made, the page cannot be saved, returning an " "Asdklf" is not registered on this wiki. Please check CentralAuth to see if it is registered on other wikis." error.

The underlying markup of the link is

<a href="/wiki/User:Asdklf;" title="">Asdklf;</a>

On testing, I can see that it is no longer possible to create user names ending in semi-colons (at least on en.Wikipedia - not tested elsewhere); however the handling of legacy accounts with such names is, as demonstrated, sub-optimal. Perhaps we should force renames?

I have not been able to find registered accounts with names ending in other punctuation characters, in order to test them.