not sure what was conflicting, but with the newest version of W3 Total Cache Version 0.9.2.5 - and the latest version of Jet Pack Version 2.1.1 - My Contact Form Module was breaking. I was getting the error "are you sure you want to do this?" after clicking submit from a previously working contact form.
I deactivated W3 Total Cache and Contact From now works perfectly.
Any idea or setting I could change, so that I could reactivate W3 Total Cache?