Hi Stefano,
Here I'm not clear what exactly you are expecting. the expected behaviour of an IAP is, the radio will be up as long as the UP link is up but if it is a Mesh point radio will be up even if it is disconnected from the ethernet. if you are expecting a Mesh point you need to meet the following,
1. IAP should have joined the cluster and updated it's image and configuration
2. Extended SSID should be disabled ( in the latest code, extended SSID is enabled by default)
Hope you got some more clarity, lease feel free for any further help on this.