I've noticed when using a Rod of Souls, I'm routinely notified that I'm picking up 1-5 XP orbs, when in theory it should be a minimum of 6 (1 + the bonus 5).

Looking at both the use function in ExtendedFishingRodItem.java and the modifyBobber function in FishingRodPropertyMixin.java, I'm seeing it set "bonusExperience" to 0, then add bonus.getBaseExperience() from any FishingBonus items in the player's inventory, and then finally set the XP with "gf_setBaseExperience(1 + bonusExperience)". Since ExtendedFishingRodItems don't implement FishingBonus, I'm not seeing any place where the rod's own experience variable would be added.