was going to make a thread about this. To add a bit more information, obtaining cooldown reduction on a charged ability incorrectly applies retroactive cooldown reduction to the time between charges, not the ability cooldown. This is inconsistent with the interaction outside of retroactive CDR, as CDR otherwise never reduces the cooldown between charges.
To reproduce this, you can use Holliday's barrel, then level it to T1 to reduce the CD, and the cooldown will not retroactively reduce. However, when extra charge is purchased, if you use one barrel, level the T1, then level to T1, the time between charges will be reduced instead. This is also how it works for other charged abilities, including Venator's grenade, which does benefit from retroactive CDR until the T3 is upgraded, at which point, with no source of additional charges, the ability will no longer benefit from retroactive CDR.
