I also encountered a similar problem when entering a "book" which should be code 4901100000 but when entering the word book on the CN22 form it suggests one option of Mind, Body and Soul or something similar. Royal Mail please get someone to check through the codes as there are at least 3 people experiencing this as mentioned on this post that are wrong.

Yes, it's pants isn't it. Unlike you, we do upload descriptions, but they do also get replaced - we recently had "Vehicle wiper blades" replaced by "Dog toy"! It seems related to the length of input tariff code - where 6 digits were once ok (as they are the WTO standard), CnD are now substituting their own 10 digits and these aren't necessarily representative of the previous entry. If 10 digits are mandatory in the system, then 1) the documentation should state this and 2) it should be an error when anything less 10 is entered, rather than some potentially bogus erroneous value submitted on your behalf that could have a negative impact on import charges incurred by the customer, or worse, refused and returned by customs particularly if you're sending to Ireland and the new code falls into the illogical An Poste banned list. As a work around, you could look into padding your current 8 digit code(s) with trailing zeros to make them 10 digits (and the same for any 6 digits codes). While this may not be technically correct in all situations, it would be more accurate then the fudge data currently being substituted and does appear to allow the entered data to be kept - I would ensure you do enter a valid description though, as that really is a requirement :)