The latest batch of boards I had from Dirty PCBs (order 2032821) have come with some really weird drilling. All holes appear to have been drilled the largest they could possibly be while keeping the minimum viable annular ring. Two oval pads have even had slots milled rather than the single, small hole specified in the PCB.
To be honest, this may well make the boards unusable as some holes are a certain size to hold connectors etc in place and I'm not sure there is enough exposed copper left to get a good solder joint to on others.
Is there any reason why the specified drill sizes would be ignored and how can I stop this happening in future?
maybe they have just rounded up some drill sizes to minimize tool changes for the panel? Or the drill size was below their minimum allowed size?
Milling slots instead of drilling sounds strange, however. Are you sure that the drills were in your excellon file, and that there was no outline for a slot in the keepout layer?