This is a lot of help. I've just taken over at a school who have supernetted in exactly the same way - changing from a subnet of 255.255.255.0 to 255.255.254.0 to double the number of IP addresses they can use. This was all working hunky-dory until we had loads of external headteachers in yesterday wanting to get online on their devices for some training.
Devices receiving IP addresses via DHCP on the old 10.36.4.* range work fine both wired and wirelessly. Devices receiving IP addresses via DHCP on the new 10.36.5.* range would only work via a wired connection, but NOT wirelessly. We have an 8 hour IP lease here, so all the nice old 10.36.4.* addresses were taken when the headteachers rocked up in the afternoon for their training. None of them could get online. Very embarrassing. This was doing my nut until I deduced that it must be something to do with the wireless controller configuration (they have a very nice, reasonably new Meru network).
The external company who came in before I started to do the IP range extension must have left out the wireless controller configuration, as it looks like the controller is still on the 255.255.255.0 subnet. The option for me to change the subnet mask on the wireless controller is greyed out for me, so I am currently in the process of getting support from Meru to sort this out. Will post back when it's fixed. Hope this is useful for someone if they ever have the same issue!