Surge of Power doesn't follow the rules of upgrade-able items, doesn't keep Extra Spirit stats.

[panvxv]

Every item which needs component to be bought is keeping it's stats.
Focus Lens is keeping Spirit Sap debuffs;
Arcane Surge, Kinetic Dash and Stamina Mastery keep the stats from Extra Stamina.

The only item which doesn't keep the stats is Surge of Power. Extra Spirit is giving +10 Spirit Power yet when we upgrade it to Surge of Power we are losing it.
Properly made Surge of Power should give +10 Spirit Power and Imbue Ability with +14 Spirit Power.

 

[steventheeven3]

Spirit Lifesteal into infuser loses 6 base spirit power

Spirit +bullet lifesteal is 160 bonus health but leech is 120 bonus health

Spirit sap loses 50 bonus health when upgrading to Focus lens, cast range gets reduced from 40m to 20m, and Cooldown gets increased from 18s to 45s

Slowing hex increases cooldown when upgraded to Vortex Web

Disarming hex has 1s less duration than rusted barrel

Healing rite upgrades into items with completely different behavior and healing amounts.


The truth is, it's not a consistent rule. But I would also wish it would be consistent instead.