I do wonder about the use of $GLOBALS. I looked up the tool from Oracle, and I see why it was added, but we already are tracking our connection in the class already, so it seems redundant and unnecessary.
I get the idea that this tool was aimed at the less structured environments where the connection wasn't necessarily available everywhere it might be needed. Since everything should go through this class, it seems like $this->conn should be sufficient.
You've spent much more time looking at this than I have. Is there some reason I'm missing?