Yeah, before we filed this Matt, we sat down and stared at it for a while and racked our brains for *any* way to make it work... and Carl suggested the same hack you did :-)

I don't think we want to go down this route -- I'm becoming less and less enamored of putting this filter into the pushdown predicate *for the particular use of this function I had in mind* -- but I'd be willing to be told that I should be more lenient.  

At any rate, we just wanted to point out the pattern and why (or, that) it failed.