Why is interest reported in Box 1 of K-1 (Form 1041) not considered part of investment income on Form 4952 and therefore not eligible for investment expense deduction?

I received K-1 (Form 1041) with a small amount (<$10) reported in Box 1 as Interest.  This amount is showing up on Schedule B, Part 1, line 1 but is NOT included on line 4a on Form 4952 and therefore not part of the amount I can deduct on line 14 of Schedule A as Investment Interest.  Why is that?