I wanted to provide an update to the bug that I discussed in my post from August 13. Oracle determined that the bug was one of a series of related bugs and our use case was just a particular slant on the main root cause. You can take a look at Bug 16191689 : SETTING HIDE_EXPRS_QKN FOR NLJ CAUSES XML QUERY TO RETURN NO RESULT to get more details and will note the multiple additional bugs that are also covered. Oracle Development investigated the issue under bug 19384287 related to our issue and found the wrong results were caused by bug 16191689. A patch is available for that bug and, when the patch is applied, the issue is resolved.
So, make sure to review not only the issue (and related bug) I discussed in my earlier post, but check out the bug link provided above and apply the suggested patch if you are experiencing any of these issues. Also note that due to the nature of how the bugs manifest, it may be possible that you are experiencing the bug and not know it. Remember that in our case we were getting wrong/inconsistent results from the same query executed multiple times. Since there was no error, this kind of issue might not be readily/easily discernible.