In "MongoDB.Bson\IO\JsonWriter.cs", line 220

var stringRepresentation = value.ToString("R", NumberFormatInfo.InvariantInfo);

need replace to
var stringRepresentation = value.ToString("G17", NumberFormatInfo.InvariantInfo);

???

In some cases, Double values formatted with the "R" standard numeric format string do not successfully round-trip if compiled using the /platform:x64 or /platform:anycpu switches and run on 64-bit systems.

https://msdn.microsoft.com/en-us/library/dwhawy9k(v=vs.110).aspx#RFormatString