R12 Asset Categories not defined for all Books allowing to select for incorrect book

We have several corporate books defined and some Asset Categories are specific to certain books. Since these are global we understand that we can pick a category while in one book and when we then attempt to attach the book there may be no LOV as the category is not defined for that major/minor.

However we now find that when we do the same in the WebADI upload it appears that it will take the combination all the way up until you submit the Posting of the asset, at which point it  results in an error.

Should this not error prior to the actual posting process?