AVR-Chat

I'm in mid-stream, porting an app from a T11 to T15.
I've hit something really odd, and it is not showing up in sim, only 
in the real chip.

I use a couple of table lookups through the Z register.
It appears that the data I get back isn't what's in the table.
Is there something I'm missing about how tables are indexed that's 
particular to the T15?

I'm using the standard setup:

clr temp
ldi zl,low(table*2)
ldi zh,high(table*2)
add zl,table_offset
adc zh,temp
lpm

Works fine in sim, but in the chip the data is VERY wrong, and 
absolutely consistent.  It could be happening after the LUT, but I 
haven't dug that far yet.