Screenshot of the bug
On Commons I noticed on a public computer (which was blocked) the block-warning when editing a page was all messed up ( [[:commons:MediaWiki:Blockedtext]] ). So the next day I asked a fellow administrator to block my current IP-address and see for myself.
However the message looked fine to me, the table MediaWiki:Blockedtext rendered fine.
So I requested another short block this time including a wiki-link (see Attachement) and there it went all funky.
Searching here I discovered this one: https://bugzilla.wikimedia.org/show_bug.cgi?id=13000
Apparantly a heading wasn't rendered in the past.
The title/summary of this bug request may be wrong as it might be specific to article-links in parameters within tables.
But because of bug 13000 it might be wider then that and may mean that any wikisyntax within parameters breaks the markup and causes the entire inclusion to be outputted raw.
If that's the case then this may be happening on quite a few places.
Version: unspecified
Severity: normal
Attached: