Sorry, I didn’t realize the change should be only for maps.
It’s possible to do this using filter ‘mappress_post_query’ instead. That filter lets you modify the results of a mashup query before it’s displayed.
However, I think it would make more sense to just add a new filter ‘mappress_poi_excerpt’ specifically for excerpts, since this issue comes up frequently – many themes & plugins modify the standard functionality.
Could you use the contact form to send a login to your blog? I’d like to add the new ‘mappress_poi_excerpt’ filter directly to your plugin, and once it’s working for you, I’ll also include it in the next release.