Weird. Have you tried changing it on the edit data source screen?
Yes, I've tried changing it at the data source screen and in the individual worksheet. Both ways are defaulted back to date/time. The data source is setup as a live connection, but I am not refreshing it. Could this have anything to do with it?
What is your data source? I've never had that revert on me.
I guess you could leave it date/time and create a calculated field: date([problem date]) and then replace the references.