When selecting multiple translations of the same content (i.e. sharing an ID), only one translation will be affected, because an array keyed by entity IDs is put into the temp store.
Select multiple translations of the same content
Apply change author action
Only one of the translations is affected, since they all have the same ID
Remove the array keys from the temp store variable
Active
1.1
Code
I've went ahead and come up with a patch for this. The entity IDs which are currently used as array keys are never needed, so removing them should fix this issue without otherwise impacting functionality.