The subject pretty much says it all. If I make changes to a configuration profile that is already installed on the devices and then click the "distribute to all" button, nothing happens on the devices, however a new item appears in the queue for each device with the status "pending".

If I manually select each device in the JSS and send a "blank push", then the queue immediately empties and the changes apply.

This doesn't affect new profiles, which seem to apply properly.