Originally Posted by une_vitesse

when we do tube changes at our shop, we inspect the old tube to try to determine the cause of the flat. twice or thrice, i've come across something strange: a slit on the inside (rim side, not tire side) of the tube, about 1 cm long, about 1 cm from the valve stem, centered between and parallel to the seams. the rims had nothing out of the ordinary about them (no burrs or scratches), the last one even had a properly installed velox rim strip.
any other wrenches ever seen this, have any hypotheses?