I wired the shield like your picture and it works fine in continuous mode. The key switches are connected to D5 and D6 though... not D11, 12. The code (KD0 and KD1) does explicitly reference 11 and 12, so I'm not sure what's going on. Maybe there's some mapping I'm not aware of?
New problem. I'm not exactly sure what is going on but these will reproduce the bug each time :
1) Select Degree mode. Enter 180.000 degrees as the increment. Press the LEFT key for 3 cycles - display will read P:-3x180.000 ; now press the RIGHT key once. The stepper will now drive infinitely and you can't get out unless you press the Reset button.
2) Select Degree mode. Enter 180.0000. Press the Right key for 4 cycles.. All works as expected; the fifth and ongoing cycles will move 360 degrees instead of 180.
If you select say 45 or 90, instead of 180, the same thing happens but at proportionally higher cycle counts - something to do with the total number of degrees or steps.
Similar things happen in Jog mode. Easier to see when the degree increment is high, like 100.
BTW.. for those building this -the lcd shield (the same part number) I received is slightly different to the above picture - there are more pins so be careful just following the pictures.