By the SOAP spec, types of "decimal" are not supposed to use scientific notation (http://www.w3.org/TR/xmlschema-2/#decimal).
However if the value of a BigDecimal is small enough, the toString() method (used by the BigDecimalType class) will print using scientific notation.
Instead, this type mapper should use the toPlainString() method to ensure no scientific notation is used.
I have attached a patch and an example to what i am referring. I don't have an actual unit test for the BigDecimalType class itself.