Last allbest was about #504, the migration from allbest to juciphox as trunk was done Sep 13th 2008. #609 is from early December.
It's possible that this was added to juciphox before this migration. I believe they are both in the same svn timeline. You could pull, build and test old (trunk back to 505-ish and juciphox branch below that) revisions from svn until you can pinpoint where things changed.
I can't think of anything in CHDK that would store images to rec viewport in play mode (or in any mode..., they all write to malloced RAM buffers), especially since you've disabled zebra, histo and edge overlay (none of which should do that anyway even with broken addresses since if I'm not mistaken, they only write their OSD overlays, not copies of images).