In the part where Pee Wee gets his bike back and is trying to escape Warner Bros police, his handlebar gets pulled off. Before it got pulled off, it had strings, but they didn't grow back. Then there is a quick camera shot of something else, and the strings are back on the handle bars, outta nowhere.
His handlebar was pulled off too, and grew back, so who's to say it wouldn't do the same for the strings? This is Pee-Wee Herman, he has all kind of weird things................