Sheldon Browns chart here: http://www.sheldonbrown.com/gloss_bo-z.html#bottom shows pretty clearly what might be going on i.e.- the right hand and left hand threads, and also the similarity of thread sizes from english to french to Italian.
I guess it pays to be careful not distorting the threads any further until its clear what the original thread actually is.

( A friend has a frame with a similar bottom bracket bracket, but it looks like someone has complicated the puzzle by managing to cut a left hand thread on the fixed side that runs alongside the existing right hand thread ! )