Appointments + Multiple Service Providers renders first timeslot Impossible

I have a single service and two service providers. Each day there's a time-slot for 10:00 am and one for 2:00pm. If "No Preference" is chosen, it marks the 10:00am time-slot as Impossible on every day, and only the 2pm slot is available.
If a specific provider is chosen, it works as expected, with both time-slots being available every day per provider. How can I make both time-slots available when "No Preference" is chosen.