the behaviour is related to a problem of the jQuery plugin (on which the Tab Grid Template is based), when loading the Google map in a hidden tab.
The desired result could be obtained in a future release of the template. The items in the WebRatio Store can be customized by the users. In this case, you can try to edit the Tab Grid Template and realize the desired result. For example, to correctly display the Google map, you could add the code which triggers the resizing of the map when the panel is showed.
Alternatively, you could solve the issue by moving the Google map in the first loading tab.