Multi-day overrides do not obey time slots.

If I want to replace a colleague who is on a 1000-1800 cover each day for a week. Another user covers out-of-hours. I click on the rota’d day and it comes up with my username, the date and the time slot. 
I expect that if I extend the dates to cover the week and leave the timeslot as is, that it will exactly replace the slots the original user was covering. 
Instead it puts them on 24 hour cover for the week. Instead I have to replace every day, one at a time (boring)
This feels like a bug to me. If the time slot is there and you can select multiple days then it should apply to each day. If it is not to work like that, there should be a start and end time for the whole period.
Is this something that is likely to be fixed or is there a workaround that doesn’t involve clicking on multiple days and doing the same thing on each.