I have just acquired a pair of Deco M4s and am slightly baffled.  I was attracted to the gigabit backhaul and the 5GHz roaming' feature but am close to 
asking for a refund because it is so limited and unpredictable.   I'll ask here first though in case I'm being silly.

Wifi channels.
Why have the units chosen 2.4GHz channel 3?   Only 3 channels are mutually isolated - 1, 6 and 11 (in UK).
The 5GHz band is beautifully clear apart from my neighbour using channel 44.  Why has the Deco chosen 
that very one?   The Android phone app told me to choose another network!
How can I configure that? 

DHCP
I have them set up as Access Points with gigabit backhaul.  I note the discussion here on DHCP in this mode but there does seem 
to be some 'intelligence' at play in that if I disconnect my DHCP server the Deco seems to kick in and 
allocate the same addresses as my normal pi based server.  This 'feature' might be useful as a backup DHCP server if only it used the right gateway address and it were documented and manageable!   Is this documented anywhere?  Is there a timescale for a management interface for this?

Dual connections?
If I temporarily disconnect a backhaul cable the Deco seems to requests a fresh DHCP lease from an interface with a MAC address one more than that on the base.  
Is it using wifi to still link up?   Does this generate a network loop when the cable is reconnected?  Where is it documented?

DNS requests
Why is it making a DNS request every 50 seconds to live.com, youtube, etc?

Any insight into these puzzling features would be appreciated.

Phil