That's what D&D needs - a consumer complaints department for artifacts.One thing here - the logic doesn't seem consistent here. Obviously you can say that "it's just magic" and wave it away, but if drinking the fire potion makes you immune (but spitting/pouring makes fire), then my assumption would be that, similarly, drinking the 'poison potion' should make you immune, too.
"Mordenkainen's Magnificient Mansion, this is Imp 127 speaking. How can I help you?"
- "That wishing flask of yours, it poisoned me!"
- "I apologize, Sir. May I know what you wrote on the flask?"
- "Erm, Poison."
- "And I presume you drank it?"
- "Yes."
- "Thank you for calling. Have a nice day Sir."