This bug was first reported 9 days ago, bumping because it was not fixed in the latest patch. When the Cursed Souvenir buff is applied to a minion with Lifesteal, the minion deals 3 damage to your face at the start of each turn, but that 3 damage does not trigger the Lifesteal like it should. Every other interaction where this occurs similarly, it cancels out ( See Zilliax 3000 with Face dmg module and Lifesteal Module)
The damage dealt is coming from the minion, however it does not give you back the 3 life like it should.
Edit: I personally encountered this when playing with Mess-Maker.