Prevent callbacks from being re-registered.
Prevent callbacks from being re-registered.

nooku/nooku-platform,nooku/nooku-platform,nooku/nooku-platform,timble/kodekit-platform,timble/kodekit-platform,timble/kodekit-platform,nooku/nooku-platform,nooku/nooku-platform,timble/kodekit-platform,timble/kodekit-platform