multiple copies print in grayscale

I have just  replaced a HP Color LaserJet 2600 with a LaserJet 2605dn and am experiencing the following strange problem.

From my lenovo G4550 Laptop, if I  print a single copy all is OK. If I print 2 or more copies, any page with colour on it prints in grayscale.  Black and white pictires and text are all OK.

I have checked for driver updates and all seems OK.

There are no problems from my HP PC.

This fault is 100% repeatable.

There were no problems with the LaserJet 2600.

I posted this to the Lenovo help forum and the consensus was  to ask at HP as it seems to be an issue with the printer, not the laptop.

Any suggestions appreciated.

Ian