It looks like the MathJax editor doesn’t always close when it loses focus. In the following screenshot, “Kripke struct” was highlighted after the MathJax editor was opened. I would expect the editor to close when I click anywhere outside of it.
EDIT: This is actually a more severe problem than I initially thought. The displayed field isn’t accurately displaying its contents. After clicking “add” the first (displayed) field didn’t clear but when I clicked “add” a second time, a warning said “The first field is empty”.
Closing and reopening the Add window fixed the problem.
Edit 2: This problem has occurred several times, now. I’ve not yet isolated what is causing it.