This sounds like a bug. We can't sort at run-time. Always imagine there are a million records of anything - sorted in memory is not an option, we need to be able to sort via MySQL index. IIRC sometimes we do have to sort at run-time but this should be only for edge-cases where we could never hope for good performance.

Assigning to you Chris. Looks like this will be more complicated to do than expected because date and date_time fields are stored as strings. So they will be sorted as such.