the AxiomSoapMessage and the SaajSoapMessage set the content-type character-set incorrectly.
The character set is surrounded by double quotes i.e "ISO-8859-1". the specification however states, $14.17 and $3.7 clearly state that this is not allowed. Although most servers do not complain about it, the one i use does
Since the implementation is not confirming to specifications, i would say it's a bug.