So when you have multiple maps on a page, there is no problem displaying them with only the shortcode and their map ID.
However, if you introduce any of the mashup functionality (combining multiple maps into one) with multiple maps on a page, weird things start to happen. Sometimes the mashup is attributed to both maps, and sometimes it doesn't show up at all.
Note1: You only need one of the maps to be a mashup for all of them to break.
Note2: This bug doesn't break the map completely, but crosses over map data in the wrong maps.