Change in bullet lists when compile

No doubt I’ve screwed some setting.

I have bulleted lists with a, b, c etc. when I compile (mobi) they change to numbers 1, 2, 3.

Lists are one of the many things that eReaders like to set for themselves. If you look at the Table and Lists section in the eBook compile format you’ll see there is a choice of None, Basic or Academic for numbered lists. If you change them you can see the differences in the preview,

However, you can edit the CSS stylesheets to override these. See section 24.18 Tables & Lists, p.661, in the manual.