I don't have this problem in 8.1.9 put when I updated to dev-master locally I had
[warning] call_user_func_array() expects parameter 1 to be a valid callback, function 'update_invoke_post_update' not found or invalid function name batch.inc:232
all over my shell when running drush updb if it included any post updates. This fixes it.
Note there are a bunch of manual includes of update.inc in UpdateDBCommands, but I think they are all still valid as they are not related to the batch, but I am not 100% sure.
Fix post updates cannot be run