Upgrading from Spirit or Bullet Lifesteal into Leech requires two slots

[Darentei]

If you attempt to upgrade Spirit or Bullet Lifesteal into Leech and you have a full inventory, the game will prompt you to sell an item in order to buy the second lifesteal item, and then upgrade. This happens even if you have enough money to pay for the full upgrade. If you have autobuy enabled, this prompt to sell can be very disruptive in a base defense situation.
Depending on your quickbuy settings and the guide you're using, you may even get a second prompt if you cancel the first one - possibly related to auto sell.

 

[connoreatspants]

Yeah came here to report this one myself. If you have Spirit lifesteal + and open slot, then add Leech to autobuy, it purchases Bullet Lifesteal, then Leech. But it functions as if you bought Bullet Lifesteal and sold it for half it’s value. Effectively costing you an extra 1600 souls.

Unsure if this is a result of the build path for Leech intending to be a combination of Spirit + Bullet Lifesteal, but isn’t telegraphed in the interface yet. But even if that is the intent, the current autobuy glitch still ends up costing the player for adding Leech to the autobuy queue.