is not an issue of the jb... those little lines are the ACTUAL jailbreak code that was injected into your iphone. Comex stored the code of the jb in the loading screen in those lines (he replaced the lines for his code basically) which is why you see it and is nothing to worry about... The other style of jb of the dev team uses another deeper method to store the jb in a completely different place (in all senses), which is why is possible to upgrade from older jbs from the dev team to new OS versions faster and quicker (in time) than new injections or hacks....