When a number is converted to a string for output to JSON there is a case where the number can be corrupted.  This occurs when the number has a single significant digit AND an exponent.  For example, the number 3E-5 is corrupted to "3E-5.0".  The affected lines are here:

https://github.com/mongodb/mongo-go-driver/blob/master/bson/bson.go#L78

And here:

https://github.com/mongodb/mongo-go-driver/blob/master/bson/bsonrw/extjson_writer.go#L624

This can be fixed this by changing:

if !strings.ContainsRune(s, '.') {

to:

if !strings.ContainsRune(s, 'E') && !strings.ContainsRune(s, '.') {

But maybe there is a better way...