Current page marker displaying inconsistently to third character

Hi all,

I'm having a strange issues whereby the current page marker on my A-Parent page only applies to the first two characters.

Basically, the traditional style numbering only applies to the first two characters, and for Roman numerals, only the first two letters are in small caps. See examples in the picture.

I've tried this with different styles (and no styles) applied, so the issue isn't to do with the style itself. There is no GREP style applied to the first two characters, or any nested style etc.

Any ideas?