When a Workflow project property is selected in the properties table, it cannot be deleted with 'Remove Property' button or converted to password with 'Convert To Password Property' button.
This functionality did work in Workflow 8.1 but no longer works in 8.5 (including RU1).
Product defect.
Workflow 8.5
Workflow 8.5 RU1
This issue has been fixed in Workflow 8.5 RU2 and newer.