As I have now traced, the change is probably associated with updating libxml2 to 2.9.1+dfsg1-4: https://packages.qa.debian.org/libx/libxml2.html
Well done Slavek. Yesterday I run a new build and I can confirm the problem on Jessie. Tonight I will try out your patch as well and report back. Anyhow before we push to git, I think we should try to find out what caused the problem. Maybe with a few adjustment somewhere, we will not need to convert all docbooks. I am a little short of time before the weekend, as already said :(
Cheers Michele