OpenCms workplace kills session spontaneously

I'm developping with OpenCms. When I log in to the workplace, and then visit a page hosted by the same OpenCms instance, my workplace session is killed, that is, the workplace asks me for my password again. This happens in a matter of secon开发者_如何学Pythonds, so I'm sure it's not because of session timeout. If I do it in 2 different browsers, it doesn't happen :\

Any clues why this is hapening?

Thanks