'Pigning' is ICMP. If it was responding to ICMP when asleep then the existing conflict avoidance already built-in to dhcpd would work. My phone is Android 4.2, so I can try it. Furthermore I have it set to disconnect when sleeping.
That's what I mean, I didn't know the DHCP server had that conflict avoidance, it should be fine :) As for your phone, one - it doesn't affect Android 4.2, and two - it doesn't affect phones that disconnect when sleeping :)
Here's details on the bug: http://www.net.princeton.edu/android/android-stops-renewing-lease-keeps-using-IP-address-11236.html
I noticed it personally the first time two nights ago, a device in DHCP leases "online and expired"