Using "Start Task" with a workflow containing an embedded script in the configuration which somehow modifies the input parameters does not update those values properly

Steps to reproduce:
1. Install the test workflow attached.
2. Create a new event using this workflow (the media used is irrelevant, no processing is done). The processing will fail or not depending on the value of the checkbox. In the "Summary" tab, note the two configuration variables defined ("donotfail" and "fail"), which should always have opposite values.
3. Select any existing event and click on "Start task". Select the test workflow. Mark the checkbox so that the workflow does not fail. Note the values of the "fail" and "donotfail" variables.

Actual Results:
The workflow fails

Expected Results:
The workflow should not fail

Workaround (if any):
The workflow fails because the variable controlling if the "failing" operation should be skipped is not the variable directly modified by the user ("donotfail"), but another hidden variable ("fail"), which is updated via a embedded script. The value of "fail" should always be set to the opposite of "donotfail".
When a new event is created, this setup works and the values sent to Opencast are correct. However, in the "Start task" wizard, the value of the hidden variable is not properly updated.