Strange. I too like Gentium Book Basic very much and did not notice an obvious change in the way it's displayed in kepubs...Could you post some pictures of what you get and, if at all possible, what you expect?
As to how to downgrade, a search on this very forum should get you there, but you'll need to get a copy of the 1.9.17 upgrade file.
Originally Posted by vorchan
This update completely messed up my fonts!
The weight of the fonts I've added is wrong, they're all to thin. Especially my favourite font Gentium Book Basic looks very wrong. The new font features (which allows one to adjust the font weight) seems to only work on the included fonts. Is there a way to fix this?
If not, how do I downgrade back to 1.9.17?