I've started a new storm wizard and I noticed that some items that add damage boost don't have the "%" in its description, it is reflected in the damage boost box that shows a " * " instead of the actual boost number. For example, if I have two pieces of gear that provides me 5% damage boost, the Damage box shows * (asterisk) instead of 5%.
If it makes things easier, I'll provide the name of some gears that got this problem:
Hardened Cap Helm of Daring Kraken's Charged Boots
These are just an example, there are other with such problems as well.
I'm guessing that the glitch is from mixing integer boost items and percentage boost items. The items you listee have an integer boost, so they will add +4 damage to spells you cast. Percentage boosts will increase damage by the percentage, so a 100 damage spell will do 101.