Digital BW, The Print

Hi - finally up and running today with my MIS VM hextone set for the 
Epson 1290 (with Pauls new curves).
Having properly purged and checked the system I have printed the 21 
step wedge on EAM and have found the following:

cool : Nicely seperated, seems very even and just what I'd expect.
 
NC : as above
 
Warm : yikes.  There is a huge seperation between the 75 and 80 
steps, almost like two wedges stuck together with the middle 
missing.  There are no smooth graduations between midtones (all of 
which seem extremely light) and the shadows - for sure this is not a 
smooth ramp.

I have checked the MIS website and confirmed I have got the latest 
curves.  Any ideas?  Do this require a curve tweak?  If so how the 
hell do I do that?

(incidentally, I loaded up the 1280 warm curve, and although far too 
dark, does not exhibit the same sharp step at 80%)