Situation:
The category needs to be changed for a seller.
The change is made in the Seller validation page.
Clicking Save does not retain the changed category, but reverts back to the original settings.

Analysis:
Dashes or spaces have been used for the sort code in the seller information found under Agency > Edit owner > Edit > section Bank details (bottom of the page).

Resolution:
HMRC can't process sort codes added in the traditional manner, e.g. 12-34-56.
Please take out all characters, which are not numbers.
12-34-56  becomes   123456

Further information:
We have amended the number of characters that can be added to this field. Only six individual characters will be possible.
This means, if you are trying to add hyphens between the sets of number, you will not be able to add more than  12-34- (which are six individual characters)