yeah the same thing happened to me. It says I have no space left on my itouch but I have absolutely no files in my itouch. All I did was install some apps.
I have an 8 gb iPod touch and used touchFree to jailbreak.
well for me i have a 16gb and it said the 50mb was gone when i no there was more space and i unistalled some apps but it still said zermb soo i re jailbroke it and it works fine again...for now