In 9cc6a60040b0f64f8ea066dd215176d4bd16621d a security patch was
introduced to prevent allocating large segments of memory when a
very large or very small decimal number was to be formatted.

As a side-effect, there was a change in formatting of small decimal
numbers even when the `decimal_pos` argument was provided, which meant
that reasonable small decimal numbers (above 1e-199) would be formatted
as `0.00`, while smaller decimal numbers (under 1e-200) would be
formatted as `1e-200`.