This happens during uploading of multiple formats (extensions) of the same weight and typeface.
i.e.: Proxima Nova Regular in .woff, .otf, .ttf, .eot
Say I upload the same font weight of different extensions, at one shot, the next step presented to me is to define the name and weight of the fonts that I have just uploaded.
After defining, I will have to select the Add Font button to commit the changes. And subsequently appear in the Installed Fonts table.
The bug occurs here.
In the table, it shows that only one font of one weight and format has been uploaded, multiple times. To further add testament to that fact, even the sizes are the same. This does not happen all the time – sometimes, 3 of the 4 would display this bug. As evident in the screencast linked below.
Contrary to this, after a refresh, it seems that the fonts uploaded just fine. The repeated font (of format and size) is the first font that a user hits 'Add Font' from.
Screencast here: http://quick.as/zDvVIqBOa
Again, a minor UX issue. But it may frustrate some users. When I first encountered the bug, it took some time for me to figure out what was happening. And I'm not the only one.