Thank you rkaufmann87 and VikingOSX for the replies. After I did the rkaufmann87 fix the problem has not yet recurred, so I cannot proceed on the VikingOSX potential fix. I am able to Control-Click on the image, see Duplicate option in the drop down menu, and select it to get a duplicate with "copy" added. If the problem recurs I will test this way to Duplicate.
I thought it was odd and worrisome that running First Aid fixed the problem temporarily (for 5 or 6 duplications) when first tried, but First Aid did not work the second time I tried it. Again, thank you rkaufmann87 and VikingOSX for your help. I hope I will not need to seek help on this problem again.