"Add" doesn't work in the new index editor

(We really, really need a group dedicated to the new index editor. I figure "Search" is the closest to a relevant category here, but it's highly unsatisfactory.)
I have now tried about six times on three different days to use the "Add" button of the new index editor to create an index entry for a line that was missed. Every time, it looks like I've succeeded....
...until I refresh the page, or come back to it from elsewhere.
(https://www.familysearch.org/ark:/61903/3:1:3Q9M-CSJ1-WS9F-3?view=index&action=view)
That's a not-insignificant amount of work that's getting lost, over and over. (I'm getting fairly practiced at it, so it only takes me about five minutes, if I don't bother with anything besides the names.)
Please fix that button, or gray it out if it's not ready yet, or something!