Output of fmt doesn't match C's printf for 'g'

I'm replacing a home grown safe format library with fmt and here is a test case where the output doesn't match:

sprintf("%g", 0.000000456) -> 4.56e-07
fmt::sprintf("%g", 0.000000456) -> 4.56000e-07

I found that FMT_USE_GRISU set to zero fixes my problem, so this algorithm appears to not generate equivalent output. 