In a model driven app I'm building, there is a business rule on the main form that says that /Deal Started Date/, a field that appears in the first tab of the form, should automatically set to Created On date if it's blank. In most cases the Deal Started Date is the day the user is inputting the form, so this makes life easier for them.
The business rule is very simple. If Deal Started Date does not contain data, then Set Field Value on Deal Started Date to the value of the field Created On.
This was working fine for months. All of a sudden, it stopped. Other business rules still work fine. Deactivating it and creating a new rule with the exact same parameters doesn't help. Using Set Default Value instead of Set Field Value doesn't help. Does a blank date somehow manage to contain data anyway and thus fail the /does not contain data/ condition? Or is there some other issue I might be able to look at to solve this?