I've been playing around with EagleFiler some more and have discovered a couple of interface bugs.
First, if I add a tag to the source list using the "+" button and doing so causes the source list to expand to the point that a scroll bar is added, my new tag will not show up. Whatever text I type is saved as its name, but visually, there's a major hiccup. If I hit return (to save the tag's name) or select another item, the view refreshes and the tag shows up as it should. I've attached a screenshot of what happens if I select the "Tags" folder, hit "+", and then drag the (newly created) scroll bar down.
Second, if I'm editing a library item's properties using the Inspector and add or delete a tag in the Inspector's tag bar, then click on a different item in the Library, everything in the Inspector window refreshes to show the new item's information except the tags. Where it gets really wonky is that if, while the new item is selected, I add/delete an item in the Inspector's tag field, the new item's tags are completely overwritten by the old item's tags.
The Inspector's tag line updates normally if I don't edit anything in it.
Although I've only tested this behavior extensively with PDFs, when I threw an RTF doc in EF exhibited the same behavior.