On my site, if I go to add media, then type "n", "b", "s" or "p" I get the non-breaking space code   appearing in front of most of my categories
There are a small number of categories that don't have   in front of them:
I've disabled all add-ons except XFMG and tested in an unedited default style and get the same results.
Initially I thought it was categories with a space in the title but that's not the case as Warframe and Destiny don't, plus TV & Movies is also fine.
I have edited some categories that have   in front just to ensure that I hadn't added a space in front (I hadn't). Editing didn't make any difference.
The issue isn't appearing in the add media album filter.
I'm unsure what the issue is, whether it's a bug or something else. I cannot reproduce it in the Media Gallery here on XenForo.