iOS AirPrint Duplex printing not working

I have setup CUPS (1.4.5) with AirPrint on my Solaris 11.3 system, and printing from my iOS devices to my HP Color LaserJet CM2320 MFP works if I print single sided, but not if I select two sided/duplex.

Printing two sided works from the host itself, and from our Macs, but not from any of our iPhones or iPads, all running the latest iOS, 10.2.1.

I've seen several similar threads about iOS 7, but no real solution and nothing for anything later.

Pulling the log from the iOS device I see this:

Feb 15 14:12:49 Thomas-iPhone-6 MobileSafari(AppleJPEG)[13147] <Notice>: [0x100a36a00] Created session

Feb 15 14:12:49 Thomas-iPhone-6 MobileSafari(CoreGraphics)[13147] <Notice>: replacing +/-infinity with -2147483648.

Feb 15 14:12:49 Thomas-iPhone-6 MobileSafari(CoreGraphics)[13147] <Notice>: replacing +/-infinity with 2147483647.

Feb 15 14:12:49 Thomas-iPhone-6 MobileSafari(PrintKit)[13147] <Notice>: AirPrint\134032HP-Color-LaserJet-CM2320-MFP\134032@\134032spiff._ipp._tcp.local .: Print-Job failed: Unsupported sides "two-sided-long-edge".

Feb 15 14:12:49 Thomas-iPhone-6 MobileSafari(AppleJPEG)[13147] <Notice>: [0x100a36a00] Releasing session

It appears similar to this thread: iOS7 duplex printing doesn't work

Ideas anyone?

For some reason this tool complains about illegal characters in my message when I paste output from wireshark and the avahi service description, so I'm attempting to reduce the contents and will add some back later.