Innate Item Bonuses not working?

[Deific Presence]

The innate item bonus system from Unchained is having problems for me. For things like rings, amulets, and cloaks which always give a fixed bonus it works fine. Once I get into belts and headband slot items where a specific ability score increase is required I run into problems. On the iPad version the option to change the ability bonuses doesn't even appear, while on the PC version I can adjust the bonus but the item remains highlighted in red and the bonus does not apply. Anybody else have this problem? Am I just missing a tab? Thanks for any advice.