Issues, Workarounds & Localization

I know it sounds ridiculous, but it's also 100% reproductible (and I have no idea how you even managed to achieve it ... come on lol):

1) make folder "test1" on your quickbar
2) in whatever 3rd party app that can use this function (e.g. http://www.evernus.com), call it (in evernus: "show in eve")
3) drag item's icon to "test1" in quickbar

#3 will seem to not be possible, but what's happening behind is that the item actually is being added - just remains invisible; to verify it:

4) make folder "test2"
5) go back to eve's native market browser
6) select some other item
7) select the item that didn't work in #3. Emphasis on: select it in market browser so it gets properly refreshed from within the eve's client. Do not use 'previous' / 'next' arrows/shortcuts.
8) drag the icon to "test2"

#8 will work just fine; now try to drag item from "test2" to "test1" - nope it won't work. The invisible one from step #3 is still happily there.

The only workaround to this bug is to delete folder containing the item. If you added something the topmost quickbar area - you can't delete it anymore (not even quickbar reset will help) - your only option is to wipe your profile file (or copy it from another character/account to save yourself a pain of reconfiguring everything).