>
> The space between the minus sign and the “<“ apparently matters.  I don’t
think it should:
>
>    < 2015-11-21 07:11:02.517785000 > - <2015-11-11 06:50:56.721641000 >
>     < 2015-11-23 05:18:35.460725000 > -<2015-11-11 06:50:56.721641000 >

You're right; it shouldn't.

I'm not working on Calc any more, though; perhaps you could send this to
emacs-devel@gnu.org