Correct on all points except my share name is 'Movies - ISO'. Every copy attempt has been to the same share.
Created 'test share' as instructed and the 40+ GB file copies just fine if I just dump it to the share AS WELL AS copying to D12\test share (tried it both ways). Copy speeds even look good @ 100+ MB/s.
I was totally shocked as I fully expected it to fail.
Is it possible this has something to do with the name of my share?
And, yes, this is extremely frustrating but at the very least we know a work-around.