this is an issue with using the map in spry tabbed panel.
to work around the problem, edit the google_javascripts/wagmp_map_1.php file.
find the following code:
var map = new GMap2(document.getElementById('wagmp_map_1'));
and change it to:
var mapElem = document.getElementById('wagmp_map_1');
var mapWidth = mapElem.style.width;
var mapHeight = mapElem.style.height;
var map = new GMap2(document.getElementById('wagmp_map_1'),{size:new GSize(mapWidth.replace('px',''),mapHeight.replace('px',''))});