Behaviour Except/When Condition does not apply

The Behaviour's Except/When Condition does not apply correctly

e.g: Adding a Field with Read Only = true, and adding the Condition: Except - Workflow Step: In Progress

Steps to reproduce

1. Add a field to all Transition Screens (e.g. Description)
2. Create Behaviour, adding the field
3. Select Read Only
4. Add a Condition: Except - Workflow Step: In Progress

Expected Behaviour

Read Only is applied to the Description field on all Issue Screens, other than when on the In Progress Transition Screen.

Actual Behaviour

Read Only is applied to the Description field on all Issue Screens

Workaround

Hard code the Behaviour desired.

E.g. for this specific example

def field = getFieldByName('Description')
field.setReadOnly(true)

if (actionName == 'In progress'){
    field.setReadOnly(false)
}