Ignore non editable workflow variables in task bulk process

The bulk process button allows to complete several tasks at the same time after filling some fields in a form where the user can set value for workflow/task variables.

The bulk process form is based on the same form that is used when only a single task is processed (from the Workflow tab of a document). Because of that and not to overwrite the existing workflow variables, only empty variables should be editable or visible (it would have no sense to display the value of one of the task whereas the other tasks have a different value).
=> therefore these fields are hidden

However the hidden workflow variables are kept in the update process and somehow it could have side effects.

This is important for the operations triggered when the task is completed like Automation chains: An example is a user who update the document title according to a metadata of the workflow => with the current behavior, all documents will end with the same title.