Wrong duration when more than 24 hours

I have a product with 1 hour duration. After the appointment has been made for 1 hour, I changed the end time manually to the next day. This should now show as ‘25 hours’ or ‘1 day 1 hour’, but instead it says ‘1 day 12 hours’.

Interesting is that when I change the actual duration to be 27 hours, it again shows as ‘1 day 12 hours’. And when I set it as 26 hours, it shows as ‘1 day’. Something is wrong with the duration calculation.