We finally solved the issue indicating an explicit version to use in the Google URL, using a v=3.5 parameter.
In Some pages, we used a v=3 parameter which indicates to use the most recent v3 version. We got the issue in those pages.
In some pages, we use a v=2 paramater which indicates to use the most recent v2 version (which is deprecated ;-)). We didn't get the issue in those pages.
Finally, in other pages, we didn't indicate a version. This says to Google to provide the most recent one, which is the v3.7 since last night, and which is a development version.
The full explanation can be found here code.google.com/intl/fr-FR/a...asics.html.
Nicolas