Steps to reproduce (at least as long as the file isn't deleted):
Go to [[de:Sereina_Trachsel]] and look at the second image ("Zieleinfahrt SM 05 in Cham (2005)"). In the wikitext the file name Datei:Zieleinfahrt_SM05.jpg is used. This exists only on commons and is a redirect to File:Sereina Trachsel.jpg.
But there also is a different local file on de.wikipedia with the title File:Sereina Trachsel.jpg.
Now click on the image to visit the description page.
Instead of the correct description page the description page for the local file is shown, without any hint that you were redirected.
File:Foo.jpg redirects to File:Bar.jpg
On local wiki:
Using File:Foo.jpg in an article shows Commons-Bar.jpg, but links to Local-Bar.jpg.
(Using File:Bar.jpg both shows and links Local-Bar.jpg, which is correct.)
Since most licenses require the correct description page to be displayed I set the severity to major.
Maybe this bug is related or even a duplicate of T30299, but though I tried to understand this bug I wasn't able to do so, so I couldn't find out if it's saying the same thing.