I've set up categories for products under the root category like so where each sub-category consists of just a letter:

Products A - E
A
B
C
D
E
Products F - J
F
G
etc...

This throws up a bizarre issue with the letter N! The left colum navigation works fine and the category list in the back end is fine but in the Catalog navigation at the bottom of the main page and each of the top level category pages the links for the K to O section appear as:

N K L M O

i.e. the N is alphabetically misplaced.

Can you suggest a fix please?

TIA

Paul