Hourly repeating tasks only shown once per day in org-agenda

[JG <jerzor@pacbell.net>]

Hi, I'm using fresh git copies of emacs and orgmode on an Ubuntu 21.10
VM with the following commit levels from git log -1:

emacs:
commit 6ecb24f877242371a0dbc7938e9b408df2690dc7 (HEAD -> master, origin/master, origin/HEAD)

orgmode:
commit 14ed651db0ef822d1b5491a376b66283da9b9349 (HEAD -> main, origin/main, origin/HEAD)

I have set up a test org file with this hourly repeating event:

* TODO Checking twice a day
<2021-12-08 Wed 7:00 +12h>

In the org-agenda I would expect to see the event appear twice a day at
7:00 and 19:00 every day, but instead I see it appear once a day at the
time in the timestamp. If I mark the 7:00 event for a day as done, I
correctly see the time stamp update to

<2021-12-08 Wed 19:00 +12h>

and after rebuilding the agenda buffer I again see the event appear
exactly once per day every day, but now at the 19:00 time slot.

I have confirmed that org-agenda-show-future-repeats is set to "Show all
repeated entries".