Adding time with addons weird behaviour

It can be reproduced here. Select the LAST slot in a day. The add the add-on option (let’s say the first one). Now, since the duration is longer than the availability, the selected slot gets changed to the FIRST in the day without any warning.

The expected behaviour would be to either show ‘no slots available’ or to select the the one available before that one with a note - as it’s easy to not see that change as a customer.