Yup; specifically, the symptoms are consistent with 'D15 RKBA=ALL 1 L' being incorrectly generated at BA 167777, causing an increment to EX.MEM, causing a skip in the DMA.
So it looks like problem with bit 12 in that carry logic; I'll check E28 and E34 when I get back to it tonight, but I have to move the machine around so I can climb inside :-) --FritzM.
