MP5 from Enchant Bracer - Mana Regeneration is not added to Mana Regen. Neither to MP5 from gear or other mana regen values.

Gear in Gear Planner:
https://classic.wowhead.com/gear-planner/mage/gnome/AjwAiUGfXPk

Gear:

MP5 stats:

Fixed in 5061ec3
A version will be released next week.