I ran into this when I derived from DocumentSummaryInformation to add a helper method to get the custom properties. It may be more useful to copy the fields from the delegated PropertySet into the wrapped one in the constructor, and then there will be no need for the 'delegate' field or any overridden methods. Then, anyone who derives from DocumentSummaryInfomation can add say their own getters to get specialized properties and freely use the fields.
Your issue is valid. However, I don't like copying field around and maintain redundant information. I am going to implement a solution which prefers accessor methods over direct field access.
Reset assignee so mails go to list.
This bug references a very old version of POI. As no new comments have been added in a long time, I'm assuming that this bug has now been fixed If the bug still exists with the latest version of POI, please re-open the bug and add a comment indicating this, ideally also with a failing unit test