Tvheadend

With an autorec rule that specifies "Days of week: Mon, Sun" (see screenshot attached), recordings are scheduled for early morning tuesday (see second screenshot attached).

This makes absolutely no sense.

What's causing this? Is it a configuration problem (did I misunderstand something in the autorec dialog box?) ? Is there a bug in tvheadend? Or is it something to do with the fact that my server is running using the UTC timezone?