Arnold, it seems to be a United ticket, and the same class, so I think it's the same kind of thing you've seen, and legit.
TexasTravelMom, thanks for the "heads up;" I'll be careful.
CL and Scudder, I don't know if it's a myth or not, but it's my husband's computer, and he doesn't want me to clear out the cookies.
I'm also getting unusual result with with other airlines: outrageously high flights with Delta (60% higher than anybody else,) British letting me do a round trip to Gdańsk, but not a multi-city returning through London; American having flights to Gdańsk that take 2 full days. Oh, and American won't let me book multi-city from either our laptop or tablet, it will from my phone. Or if I go through Google flights.
Weird. And frustrating. It seems like I'm spending way too much time on this.