can't tab from hours to minutes in event editing dialog

I'm running gnome-calendar built from git master on Ubuntu 20.04.

In the event editing dialog, if I click in the hours field and enter a number, I would expect to be able to press Tab to advance to the minutes field. But that doesn't work - if I press Tab, the edit cursor disappears and it's not clear which field has the focus. It's not the minutes field, since if I then type digits they don't appear there.

So to enter hours and minutes I must click in the hours field, type a number, then go back to the mouse and click in the minutes field. That's inconvenient.