I don't know what brand tube you are using, but it is common for most tubes to be narrow at the valve stem area and then bulge out slightly. I always give up when there is a problem around the valve stem. It is possible that because you patched in the bulged area, that the tube stretched unevenly and the patch didn't hold. Also, personally i never use those presta valve nuts, because when you tightening them (and especially when you tighten them as tight as possible). you can actually pull the valve right out of the tube. Hope this helps. brian