Alejandro,
Sorry for the delay. We've done a bit of testing, and can't replicate the problem you're having. When we set our Canvas to a Fluid height, Facebook sets the "scrollbars" setting on the iFrame it uses to 'yes'. When that is 'yes', the scrollbars will show if the content is larger than the display area.
On your Application, the iFrame scrollbars setting is 'no'. I'm not sure why that's happening to your application, but we're trying to determine the cause.
I may try to setup our demo application in that manner to show you that it can work with JFBConnect, but even that, that won't explain why. Please verify your settings, or even try different ones. Also note that in browsers like Chrome, the scrollbars won't actually appear. You will be able to scroll, but the bars are actually hidden until the user starts scrolling within the frame.
Hope that helps, but let us know if not,
Alex