At the top of the Social Security worksheet, where you enter the amounts, there are boxes to check if taxpayer resides in certain listed countries.  A gremlin must have checked that box when you weren't looking. 

Say what you will about paper returns, but preparing them correctly is easier for me if I have something in front of me that I can review, like in the good old days, to check if it passes "the smell test."  Does the return itself show Social Security amount received on Line 6a?  What is the AGI?  If I see $30,000 Social Security with 0 taxable and $50,000 AGI anyway, it's going to jump out at me.  Maybe it would, looking at a screen too, but I'm an old dog not good at learning new tricks. 

Another feature that might have avoided this is to use the "two year comparison."  Were these new clients?  I don't have any new clients.  I should always check the two-year comparison, but sometimes I don't until I have printed out the paper return.