Hi Carlos,
I noticed this problem before in other situations. My understanding
is that city names are collected from different sources, sometimes we
have additional info from a POI, sometimes we don't. If I got that right
the index will have two entries when a city name is derived from e.g. the
housenumber processing. I don't know why this is done, but their is special
code for this, so it seems to be intended.
I don't know why you see the problem only with the extra rules. Maybe
a different spelling in e.g. one addr:city ?
Gerd