I find setting the Root Reference is generally a bad idea.
When you deploy a schema with Root Reference = (Default), each root level element in the schema is registered as a message type.
In your case there will be 4 message types: POLLINGSTMT, ArrayOfPOLLINGSTMTRECORD, POLLINGSTMTRECORD, POLLINGSTMTResponse.
If you specify the Root Reference then only that element is registered as a message type, i.e. POLLINGSTMT
When the Xml Disassembler receives a message that is an envelope it debatches each child of the Body Xpath node and tries to find the message type. If you have set the Root Reference it cannot find the message type, which is why you need to create your separate schema.
A simpler way of enabling debatching, staring with the generated schema:
1. Select <Schema> and set Envelope = Yes
2. Select POLLINGSTMT and set Body Xpath = POLLINGSTMT/POLLINGSTMTRECORD
There is a potential issue if you ever expect to receive a POLLINGSTMTResponse message using the Xml receive pipeline, but in your case this should not happen.