Kernel 3.17 no longer allows bonding ppp devices

Hi, I hit a problem when attempting to upgrade to kernel 3.17.2 on a particular server. Some time between 3.13 and 3.17, the bonding driver has stopped accepting ppp devices, instead throwing an error that the MAC address cannot be changed. (And does not allow this to be forced) I suspect it's unlikely.. but has anyone here encountered this issue and found a solution? Alternatively.. do you know where the right place to file bug report about this would be? It's been a while since I've filed anything against the linux kernel itself. Cheers, Toby