MediaViewer can use an (imageurl, width) pair to generate an image URL with the correct width. When the input URL is a full-size image, and the output is a thumbnail, and the domain/URL prefix (repo zone URL) is different for full images and thumbnails, the generated URL will be incorrect.
Version: unspecified
Severity: minor
Setting to low priority: this does not affect WMF servers, nor any server that uses MediaViewer with its default configuration (specifically, with $wgUseThumbnailGuessing = false).
(In reply to Tisza Gergő from comment #1)
(specifically, with $wgUseThumbnailGuessing = false).
That's $wgMediaViewerUseThumbnailGuessing of course.
Mass-removing the Multimedia tag from MediaViewer tasks, as this is now being worked on by the Reading department, not Editing's Multimedia team.