Hi christophe,
I'm not sure if this is the right solution for you, but could you try the following steps:
1. In your form, click Tools > Form Options
2. Click Versioning. Inside "Versioning" category, there is an option to manage version upgrades. The option "Automatically upgrade existing forms" is selected by default. Can you try selecting the option "Do nothing"? Then re-save your form.
3. Re-publish your form to your library and see if that works.
More information here: http://office.microsoft.com/en-us/infopath/HA100522701033.aspx
Or you could try Patrick Halstead's idea of creating separate views for each version and add an Open rule to switch to the correct view based on the version in the form. You can read the post here.