When in Remove (5), field "From": I fill in "12" (manually, not with arrows), then <TAB> to "to" field: there I fill in "34". At the moment I enter the 3, the "From:" field will change to "3" and the "to" field will properly be filled with "3", later with "34". Works with other combinations too, of course. I did not try for other fields.
Firefox 64 bit on Windows 10.