[Plugin: W3 Total Cache] CDN url replacement stops working

Hi,
First of all, I would like to thank the developers for the great plugin. I am fairly new to WordPress and I was at first disappointed with it’s performance compared to other CMS’s I am used to, until I found this plugin.

However , I have a problem getting W3 Total Cache to work with Amazon S3.
I have set up the CNAME settings correctly, uploaded the theme, wp-includes and minimify files and the plugin successfully replaced all the URI of theses files to my subdomain that I created for s3 (s3.mywebsitename.com).
Two days later, I comeback to visit my website with my browser and surprise: the files are no longer pointing to s3.mywebsitename.com but to mywebsitename.com.
I tried disable / re-enable CDN settings in W3 Total Cache and clear the cache, no luck. Then I decided to remove the plugin and re-install it, that did the job and the files addresses point to s3.mywebsitename.com.

Two days after that, I comeback again and the same story again, my files point to my main domain instead of my s3 subdomain.

What is the problem, how to fix this?

I am running WordPress 3.0.3 on 1and1 shared hosting and using Amazon S3.

Thanks
Happy Holidays!