I ask only because my Armor Penetration is the same at 43 and I could increase that with some G12 pieces. My Defense Penetration on my G12 Boba Fett is currently at 0% and I'm not even sure how to increase it...again which is why I said this could be hard to calculate even if it wasn't a visual bug since there are not clear formulas to calculate what "Defense Penetration" does anyway.
"Ignores a percentage of enemy's Defense" is fine, but when there is no clearly defined "Defense" stat like there is for Armor, Protection, Health, etc. it's a little muddy what exactly this is ignoring. Ignoring Armor, Protection, Health, a little bit of all...?