Apple configurator process

On a MacBook Air I installed Apple configurator to manage an Ipad mini with iOS 8.3.

Also Apple configurator is fully up to date, version 1.7.1.

After making a setting in the preparation tab including supervsion ticked , I click Prepare and confirm with Apply when asked if all USB connected devices should be prepared.

I have one device connected to which the MacBook sends some commands (takes about a minute) .

After this minute in the top of the configuration App , the number 1 (1 device) is moving from the preparation to the supervise tab.

At this point, in order to move on to the supervision tab, I first have to press stop in the preparation tab.

There's no confirmation of the device connected being ready with the preparation , so.....

Is this "by design" or what do I have to do to get to the next tabs (supervise, assign) ?