Hello Bill,

SMOBC is pretty much SOP these daze (pronounced days). I will be less than mainstream in saying they should have supplied reflowed tin/lead without solder under mask.  If it were me (fabricating) I would have called to say I need allowance for up to .004 under solder mask (adjacent to exposed copper).  
One cannot mistake "Copper Plate" and once in the reflow mode; solder mask over molten metals is #1 concern.  I speculate that what you have is OE; Operator Error.  I would call and talk with the QA person and put it to him (these folks are cursed with a consciences and their ID requires them to fess up).  The business part of this is that -nowadays (pronounced "now-A-daze") there is very little profit in these boards; not enough to be giving two for one's if you don't need to.  Some amenable compromise is always best (discount coupons for future orders), and it will build very strong relationships.

I refer to the solder configuration of your parts as "Selective Tin/Lead Strip Reflow."  In the ole days tin/lead was used as a resist because it was quickly "reflowed" over a huge pot of boiling oil (well, very hot)resulting in the beloved "solder" coat.  There were volumes written on solder mask design over molten metals.  Today very few use tin/lead as a resist; some use tin, but why go through the extra time of lead.  For hasl/smobc all the resist is stripped off, then slober mask, then across the Hot Air Solder Level.  For Solder Plate (aka Tin Plate or Tin/Lead Plate or Tin/Lead Reflow) one would Tin Plate THEN lead Plate to exact numbers (PbSn 62) THEN "Selectively" remove the unwanted Tin and Lead Platings, then Solder Mask and THEN reflow.  Hence the term "Selective Solder Strip" (aka Selective Tin/Lead Strip, etc.)and the need for the .004 (registration of solder mask).  So in your case, OE.  BTW, SOP is Standard Operating Procedure.

OK, OK, now about the crack about forty-something being old...

Good luck,

Brad in Boston