So you don't waste time looking into this: QB2012 Desktop Mac DOES update a file that was opened from a mounted partition. I am embarrassed to say, as I was playing with the files and getting ready to put QB2019 in place for prod, I cleaned out the partition and didn't have problems when I opened the file from the partition. I was certain I had checked this, but could not reproduce the issue. I even tried upgrading the QB2009 file from desktop and putting it into the partition and upgrading the QB2009 file from the partition and leaving it in the partition. Both worked ok. So, I have to believe it was my problem that the partition did not have enough space.