Okay I figured out the problem.
So actually, what I tried over and over (and what you told me) is correct, and works. Unfortunately, there seems to be a bug in the display where it LOOKS like it doesn't work.
When I enter $0 and save it, in the resulting page, it just pops back to $1200. So it appears that it did NOT save my $0 input. Which led to my trying over and over, and everything I do being seemingly futile.
However, if I just ignore the $1200 displayed and proceed all the way to the "File my tax return" section again, when I examine the PDF... lo and behold... the $1200 was in fact removed and the 5329 is no longer part of the documents to be filed.
That is a horrible, frustrating, time-wasting user experience. And I only got lucky and progressed past this frustration by hypothesizing that the bug might be only in the display, but no bug in the actual filed/created documents. Someone who trusted the software more might just get stuck in an endless loop of try to save $0 -> unsuccessful, try to save $0 -> unsuccessful...
Anyway, thanks for your time!
