So, I found something.
I decided to come back to the officiel website and, in the description of the template, it's written:
"New: Inbuilt CSS and Javascript Compression"
So, I thought, it might be something to do with our problem.
In the template menu, there're multi setting:

When I put "Optimize JS" on "non", everything was fine.
But I didn't really understand this setting, and I don't really know the consequences of this option. In practical terms, what's going to change ? (except that Jcomments works now!

)