I have never heard of this with our wheels but I have personally seen it happen on a Nissan before. Cracked all the way right through the center of the wheel, we were offroading. They were a 15-16" wheel with descent rubber, never seen/heard of it happening until then.
But as Mr Crowley mentioned use some soapy water and make sure it the rim before buying another. With the above situation it was VERY obvious that it was cracked, so I am leaning towards the shop just not finding the hole.
2001 Ironman Daily Driver... 3.5" suspension lift (OME912 springs and 1" spring spacer), ball joint flip, 1.5" front diff. drop, 33"x12.5 TrXus MT, 16x10 Eagle Alloy rims, Interceptor, PV muffler, K&N air filter, Alpine Supercharger, Bilstein shocks, and some trimming.
2000 Ironman Project LS-1 VX... very slow progress but someday....... ohhhhh someday......