Assert.AreEqual(16, 
               BigDecimal.Parse("9999,9999,9999,9999".Replace(",", ""))
                           .StripTrailingZeros().Precision);

It fails, with the actual value being 17 ... Yikes! Something to do with StripTrailingZeros ...

I've also seen issues with unnecessary rounding, when Parsing strings with a MathContext with a precision of 16, and where there's only been 16 digits. Probably negative numbers, cause I've seen negative numbers created using a big integer constructor, with a Precision of 17 when there's clearly only 16 digits, and that when you Abs() the value the Precision is 16.

I'm using <package id="dmath" version="1.5.66" targetFramework="net45" />

I feel like this package needs a lot more testing? I don't really have the time at the moment.