Un-able to modify "Category" field for existing Scheduled Requests

Un-able to modify "Category" field for existing Scheduled Requests

When I try to modify the "Category" field for an existing scheduled request I cannot select anything. Also the field doesn't display the category that had been set.
When the scheduled request runs it does fill in the category. 
If I create a new scheduled request I can set the "Category" field.

Can you please help with this issue?  
Best regards,
Allistair

PS. I am running Build 7909 on a MSSQL 2005 server

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