I've had the joy of working with a SOAP endpoint that doesn't recognise <element /> syntax, which left me having to create attributes assigned to '' in my Python code, so SUDS would generate the <element></element> syntax for me.
They also massively over-engineered the endpoint, constantly wrapping elements within elements, for no real reason.
That's always annoyed me: sure, XML can be heavyweight but if we're going to use it we should at least get the benefits.
Naturally that line of reasoning didn't get very far with the “maintainers” of an internal purported-SSO system with a SOAP endpoint which crashed on non-ASCII data or SQL special characters in the submitted username / password values.
They also massively over-engineered the endpoint, constantly wrapping elements within elements, for no real reason.