Ah yes, the old DID rims.... They 'always' split on the joins (usually next to the little silver DID sticker) and sometimes in other places.
Check carefully - my 125D's front wheel had literally dozens of cracks in it - some were tiny, some were medium-big.
I've just had a YZ125X rim re-welded, mostly as an experiment. It took a fair bit of time with the die grinder and then the sand-paper to get rid of the big lump of weld on the visible surface, and it still isn't 100% (I just got impatient).
The weld is a slightly different colour than the rest of the rim too - definitely not a problem for a race bike, but probably no good for a lounge-room bike.
Having said all of that, I own an IT rim that's been welded up, and then someone has hit something hard enough to put a big flat-spot in the rim at the weld. The weld has held, so it seems obvious that a good weld is fine.