At https://commons.wikimedia.org/wiki/Category:Wikimania_2013_DevCamp?useskin=monobook I'm getting the following in my browser's error console:
I'm not sure why.
Version: wmf-deployment
Severity: normal
URL: https://commons.wikimedia.org/wiki/Category:Wikimania_2013_DevCamp?useskin=monobook
When a dialog box appears at https://www.mediawiki.org/w/index.php?title=Talk:Flow&workflow=050b8fe7de9310412404782bcb0873b9, I'm getting similar errors:
GET https://www.mediawiki.org/wiki/Images/ui-bg_flat_75_ffffff_40x100.png 404 (Not Found)
GET https://www.mediawiki.org/wiki/Images/ui-bg_glass_75_dadada_1x400.png 404 (Not Found)
GET https://www.mediawiki.org/wiki/Images/ui-bg_flat_0_aaaaaa_40x100.png 404 (Not Found)
GET https://www.mediawiki.org/wiki/Images/ui-bg_glass_75_e6e6e6_1x400.png 404 (Not Found)
GET https://www.mediawiki.org/wiki/Images/ui-bg_highlight-soft_75_cccccc_1x100.png 404 (Not Found)
This is while logged in, using the Monobook skin.
We have a theme also based on Monobook, and are facing the problem.
When the CSS gets minimised and the image paths changed or embedded, for some reasons some images are neither embedded or with their path fixed.
I am getting this too with MonoBook on a MW 1.23.13 Never seen this issue before so I guess it must have been either MW 1.23.12 or MW 1.23.13 which introduced this. I am not solid on this though.
Hmm, after updating my browser from Fx 43 to 44 the issue disappeared. However, it may also be that just closing the browser helped for me. Pretty strange.