Camera doesn't fire callbacks if the targetWidth/Height are set and the source is camera. Other combinations seem to work OK.
Not sure if this is relevant, but this is what gets outputted in the console:
2014-09-30 16:43:41.136 eEcosphere[351:50878] Snapshotting a view that has not been rendered results in an empty snapshot. Ensure your view has been rendered at least once before snapshotting or snapshot after screen updates.
This has been thoroughly tested.