problem with upgrade to HPLIP 3.18.10 - unable to print in black and white

I have just completed the upgrade to HPLIP 3.18.10 for use with my HP Laserjet CP 1025 on Mint 17, as recommended. However, it is not allowing me to print in black and white. The following observations might help with diagnosis:
1. There is plenty of black toner and, if I select print in colour, the black is used without any problem.
2. There is not a problem with the printer as, if it is connected to my laptop, which runs Windows 7, it functions perfectly in all modes. Therefore, must be an issue with the drivers?
3. The printer was working fine before the upgrade.
4. If I try to print in black and white using Mint 17, I get blank sheets of paper.
5. I have tried running "hp-check -t" to see if there are any error messages. There are not.

Subsequently, I have tried "uninstalling" 3.18.10 and reinstalling the previous, working version but the problem persists.

This upgrade to 3.18.10 has rendered an expensive piece of kit totally useless.

Any advice welcome.
Thanks