Since today, Google returns 400 Bad Request for StaticMapService.GetMapImage.
As the regular google examples work perfectly on my box, I assume that Google has changed something within their API, causing incompatibilities with ExtJS.ux.GMapPanel3 (haven't tested with v2 so far). I am using the recenter-map example to test, with the stock GMapPanel3 from your repository (without my changes).
I noticed that on the StaticMapService.GetMapImage, there are parameters sent as such:
1iNaN:
2iNaN:
If using the google examples, there's no single call to StaticMapService. Not sure where this comes from.