User is able to create non catalog request with natural account mapping set - how to avoid this?

Summary: user is able to create non catalog request using a natural account mapping set value, instead of a valid Category from Category LOV - ie user is able to type it in as shown below:

We do not have a Category named "Printing", but we have a natural account mapping Set with a label = Printing as shown below

user is able to create the non catalog request, but it does not route correctly to any approver (as expected) .

why is this occurring and how to avoid it from re ocurring with this or any other user.

Version (include the version you are using, if applicable): 25C with Redwood Requisitions