Thank you, thank you, that must be the cause!
FYI though: when I went back and deleted and re-entered my 1095-A, I marked "No" when asked whether I received unemployment (just as a test, in case what I thought was a glitch was related to that).
Answering "No" did not change the result of line 5 on form 8962. TT must ignore that answer and actually look to see if unemployment benefits were included in the Income section.
