GMail free storage counter seems to be having a small bug which initially shows an incorrect value and displays correct value after couple of seconds.
The following are the two screen capture of GMail web site, one grabbed after immediate launch of the site and the second one after few seconds. The free storage counter initially shows GMail storage capacity as 2757 MB and after couple of seconds it updates to 4642 MB(when I grabbed the screen).
You can also notice this if you carefully observe the free space counter of GMail. Try now.