The MediaWiki do not allow use some characters in article titles for technical reasons, precisely from this regular expression .*[?&]+[^=]+=[^&]+.*

Although articles titles with these characters are forbidden, they are allowed in internal links, for example, [[?curid=1234]] will link to the article with curid 1234, and despite this will work, it will have a red link, because no article with this title exists. I think it is useful, I linked a diff once in this way in a summary edit at pt.wikipedia.org/w/index.php?title=Igreja_Universal_do_Reino_de_Deus&diff=prev&oldid=4180672 and also in my sandbox at pt.wikipedia.org/w/index.php?title=Usuário:Luizdl/Testes&oldid=41829286

These kind of link could be useful, it obviously is a bug just because it has a red link, also, the link created has the parameter action=edit, and these links only work because it also pass the parameter redlink=1 which makes the article don't enter in edit mode because "article exists". I think one of two things could be done on this issue, or make internal links with these character don't work, or make them have a blue link.