Has anyone managed to use the webservice to update PO and update the item revision?

We are testing the PO Webservice to update a PO.. Everthing works fine... until we try to update the item revision <ItemRevision>A</ItemRevision>.

We've completed a trace and for some reason the revision is a number field, rather than character.  Has anyone come across this.

Here's the call we are making,

<soapenv:Envelope xmlns:ser="http://xmlns.oracle.com/apps/fnd/ServiceBean" xmlns:ser1="http://xmlns.oracle.com/apps/po/service" xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">

<soapenv:Header>

<wsse:Security soapenv:mustUnderstand="1" xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd" xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd