This is a new feature, so there will be odd problems. Some problems are a direct result of what is provided by the Google Map interface. Some will be fixed or avoided in the future.
Conference Locations -- Click to see details. Note that the Google Map interface has a strange limit on geocoding. Consistently the 12th item is rejected as over the quota (depending on the list, CVPR 2011 is the 12th conference for the month). Out of 20, you lose 2-3, out of 30, you lose 8-9, so it is not completely predictable.