Required Setups for Item Structure UOM other than primary for Discrete MFG

A few forum posts and Oracle documentation mention that, while in the initial creation or upload of an item structure, the values for Quantity are in Primary UOM. However, afterwards, we should be able to change the quantity and UOM to any "convertable" UOM or one where a "valid conversion" exists.

It works fine for conversions within a class which have a standard conversion setup, but it does not appear to work between classes even with an interclass conversion set up, and after running collect order reference details, in either single or dual uom tracking. It provides error that UOM is invalid.