We can get into "radio recovery console" mode fine, and after pressing the "boot-default mode" button (before the countdown is done), it says it is rebooting into default mode. Unfortunately, it actually reboots right back into radio recovery mode.
Same behavior for both units we have on hand, while the 450b's go into default mode fine (using instructions in this thread, though we discovered that its best to hold them for just under a second to reliably get them into radio recovery mode).
Not sure what's going on there... we will try to reproduce this behavior.
With regards to your other comment, yes, various hardware reacts a bit differently to the timing of the "apply power", "remove power" sequence. Good note for others!
Can you provide a screen shot of the recovery page. I see in the header the mention of 15.1_4. I am looking for the current software and backup recovery files listed.
What I noticed was there was there are no Backup Recovery Files. I am not sure what issues that could cause but could be related. Upgrade to mimimum 15.1.5 which will also load it as a Backup Recovery File and you should be set. If you still have issue, please let us know.