Hookpad - SHIFT+letter does not result in the note lengths being added, but replaced instead

I tried to hold down Shift plus a letter, but it wouldn’t add the lengths together like it would a month ago. Now I have to click on the length I want to add while holding Shift (or after clicking +).

My setup: Firefox 55 32-bit on Windows 7 64-bit.

Reposting since I don’t think my previous post adequately described/captured the bug.