The sort key of the style needs to be fixed to provide two separate sort keys, one for contributors and one for the date. In the new processor, when a macro that contains a date is provided as a sort key, the date will be extracted and used as the sort key, with the rest of the macro output being ignored -- so it's doing exactly what it was designed to do here.

The fix to the style is very simple; if someone else doesn't beat me to it, I can take care of it this evening after dinner (two or three hours from now).

I've checking in changes to the sort keys, which seem to work okay. The new version of the style will appear soon, after it is cleared by the core team.