ASM Custom Response Page XML SOAP REST

Hello,

I have trouble with customised response page from f5 ASM :

My Custom Default Response page will send a 403 HTTP Code

My Custom XML Response page will send a 500 HTTP Code for every non allowed XML request.

But in practice, it's not what is happening :

when a SOAP XML request is sent with an XML error => It shows 500 HTTP Code . All is OK at this step.

But when a REST XML request is sent with an XML error (exemple : WSDL is not valid or XML Malformed Data) => 403 HTTP Code is Returned instead of 500

Do you know why I have this results with SOAP and REST ?

Is this the right way to do customise response page or do I need to write a specific iRULE for REST XML errors in order to return a 500 HTTP CODE ?

Regards