mustUnderstand use when upgrading from Axis 1.1 to 1.3

["McCarthy, Laura" <La...@fmr.com>]

Hi all, I am a non-programmer trying to sort out an issue, so bear with
me.  My firm hosts an API using SOAP 1.1/Axis 1.1 and we have one client
trying to upgrade their platform to Axis 1.3.  When they send us API
requests, they are getting the error "Did not understand
"MustUnderstand&quot" when they receive our SOAP response. Our SOAP
message to them includes mustUnderstand="false" and they think that they
are getting the fault because we should be sending mustUnderstand="0"
instead.  I did read that there is a new "MustUnderstandChecker" as part
of Axis 1.3 that was not part of 1.1.  Their app does not throw this
error when they were running Axis 1.1
 
So, couple questions if someone can help: 
 
Would our outgoing message pass their "MustUnderstandChecker" validation
if we changed to use 0/1 instead of true/false?  
 
If yes, would we have to upgrade to Axis 1.3 in order to send the 0/1
values or can that be done while we stay on Axis 1.1?   I assume that
would be backwards compatible to other clients running Axis 1.1 because
they are not doing the validation at all? 
 
Final question -- given that the 0/1 values are the SOAP 1.1 standard,
is there any other reason why true/false values must be used?   Are the
true/false values the default used on the Axis 1.1 platform?  I am
trying to understand if this is a fundamental interoperability issue
between Axis 1.1 and 1.3 or if it would have been an explicit decision
to use true/false.
 
Unfortunately, we can't really tell the client to change their code to
allow for this/ignore the fault -- they are just telling us that we are
sub-standard because our API does not support use by a Axis 1.3 client.
Best way to proceed? 
 
Thanks VERY much, Laura.