Hello,
Could you please describe the issue in a little bit more detail, what steps do you take when configuring the new AP interface, what settings are applied, for example firewall zones, wireless security (cipher/encryption), any changes to advanced settings?
As for the configuration in general, all interfaces are reloaded whenever a new wireless interface is added or when some modification is done to any of the wired interfaces - this is the intended behavior. Additionally, if there is an error with any interface configuration, it will not turn on until the error is fixed. If you've configured your interface correctly and it still doesn't come up, please generate a troubleshoot file and send it to me via private message, I'll make sure to investigate the issue.
What is a troubleshoot file and how to generate it:
A Troubleshoot file contains a device's event logs, configuration files and other info useful for diagnostics. It can be downloaded from your device's WebUI, Troubleshoot page:
System → Administration → Troubleshoot
Best regards,
Tomas.