[Help? Page layouts are being 'rounded off'. I need it precise for book printing.]

I just received the update to version 1.10.0.1127

It's the first time I've had this issue. I'm creating a custom book cover template for a client, and his printing company - Bookmobile, specified the spine width as being 0.8497 inches. When I enter this in, and continue to the next measurement - Affinity Designer and Publisher - round it off to .85.  I tried converting to millimeters -but it's doing the same thing.

 

Aside form going back to an earlier version, is there something else that can be done?

 

Thanks,

 

Rebecca