I tend to doubt there's anything weird with the welding on the BB shell, this looks totally typical of a common welded BB shell. You might see no signs in the interior of the shell cause it's a tight thin line (obscured with threading and dirt) where the exterior was ground with a "V" groove and filled with very visible weld metal. No idea who made this frame (probable non-original fork) but juvela seems to be hot on the trail! If that runs cold then MauriceMoss would be the next best sleuth to take it on.