I am having the same problem with the NEW version of Google Maps. Note that this does not apply to the public version of Google Maps, but only the invite-only new version with a URL that starts with https://www.google.com/maps/preview
Sometimes entering a lat/long will get me a marker, but that marker will be of a nearby landmark and not the actual GPS coordinates. I'd love to know if anyone knows anything more about this.
Here's an example URL: https://www.google.com/maps/preview#!q=49.0000%2C+-15.0000&data=!4m10!1m9!4m8!1m3!1d25953255!2d22!3d49.5!3m2!1i1280!2i939!4f13.1
if it redirects you to this url, it will work correctly because you don't have the new maps: https://www.google.com/maps?sll=49.49998453495486%2C21.9400958520269&sspn=42.82324958915673%2C68.40461053396893&t=m&q=49.0000%2C+-15.0000&output=classic
