Service provider list is not updated with changed Service automatically

Hello,
I am not sure if this is by design or did I miss anything:
on my website http://www.etosteorelief.com/
If I change the "Service", the "service provider" list won't get automatically updated, I must click on the "Show available times" beside the "Service" and then the "Service Provider" dropdown list will get updated.
Can this be made automatic?
Thanks.