you can see this bug on your website http://www.atlsoft.de/google-maps-gpx-viewer/
if you switch from google maps to osm there is also shown google's lincense and only a trivial link to http://www.openstreetmap.org
Our requested attribution is "© OpenStreetMap contributors".
You must make it clear that the data is available under the Open Database Licence. This can be achieved by providing a "License" or "Terms" link which links to http://www.openstreetmap.org/copyright or http://www.opendatacommons.org/licenses/odbl.
please fix this and i'll buy you a beer ;-)