PDF Table used for layout - Passes Accessibility Checker, but shouldn't?

I have a PDF that was sent to me by a colleage.  The document has a table that was used to layout a form and it is irregular, has no headers, merged cells with no colspan, but the accessibility checker in Acrobat is fine with it?  It throws up no errors about headers or regularity or any of those problems I would expect.  I'm experiencing the same in Pac3.  While Pac3 has errors, none are about the structure of this table.

Does this sound like a glitch, where it is overlooking this poorly tagged table? Does PDF have the concept of an ignored "layout table" that I don't know about?  

I am attaching a screenshot of the tag structure of this table, to facilitate discussion of what I mean.