I thought I was going crazy, but there's something wacky with the ParamType isIn() method....
isIn() is true for output parameters, and false for inout parameters 
From a ViewModel extension function:
this.config.paramDefinitions.forEach { (param, type) ->
logger.info("$param (${type.name}): isIn() => ${type.isIn}, isOut() => ${type.isOut}")
}
v8.1.40