How to NOT Default Task Status value on Assignee Change?

We do not want the Task Status defaulting to a specific value when the Assignee value is changed. We want the current Task Status value to remain for that task when an Assignee value is changed. I verified Profile Options Task Manager : Default Task Status and Task Manager : Default assignee status are now null (used to be set to Assigned.). But now when I change the Assignee, I get error msg:

No trips found for the resource xxxx (Employee Resource, xxxx) between dd-mon-yyyy hh:mm and dd-mon-yyyy hh:mm. Task status is either disabled or invalid. Please enter a valid task status.