Continue numbering function stops at letter C.

I have a numbered (lettered) list of A, B, C, D,... but the list will not continue past letter C. I have created the 2 styles for numbering, one starting the number at letter A and one continuing from previous list. When I use the continue from previous list style it works up until letter C. and continues letter C. for the remainder of the list, for example:

A. TOPIC (start at A. paragraph style applied)

text text text text text text text text text text text text

B. TOPIC (continue numbering paragraph style applied)

text text text text text text text text text text text text

C. TOPIC (continue numbering paragraph style applied)

text text text text text text text text text text text text

C. TOPIC (continue numbering paragraph style applied)

text text text text text text text text text text text text

etc.

I'm not using styles existing from a previous document, am not using styles based on other styles and have made all styles from scratch so I'm unsure why the numbering isn't working.