Tempered doom weapon bonus not as described

Platform, device version and operating system:
Steam, Windows 10

Screenshot or image:

What you were expecting to happen, and what actually happened:
Card says +2 per Tempering level. Weapon is tempered to level 8; 2x8 s/= 16, but boost is only 8.

How often does this happen? When did it begin happening?
I’ve noticed this the past few weeks, on various doomed weapons, in various events.

Steps to make it happen again
Use a tempered doom weapon in world event, PvP, or explore. Check the bonus calculation.

Boost ratio is for gem creation ([4 brown allies + 0 brown enemies] x 2 =8 ) not for weapon damage.
Extra damage from tempering levels is never shown on any tooltip, you have to add it in your head.