Collectible Card Game Headquarters

Describe the Bug:
I have two Jet Medallion and four Swamp on the battlefield. I cast a Drain Life and tap all available mana. X is 3. fixed

Which card did behave improperly ?
Maybe Drain Life. More likely the cost reducing engine.

Which update are you using?(date,name)Which type(Duel,Gauntlet,Sealed Deck)
FRF.

What exactly should be the correct behavior/interaction ?
X should be 4. I can't find chapter and verse in the comprehensive rules, which is supremely irritating, but rulings from the two cards:
Jet Medallion: 10/4/2004 The generic X cost is still considered generic even if there is a requirement that a specific color be used for it. For example, "only black mana can be spent this way". This distinction is important for effects which reduce the generic portion of a spell's cost.
10/4/2004 The effect is cumulative.
Drain Life: 10/4/2004 Cost reducers can be used to reduce the X part of the mana cost.

So get from the swamps and reduce cost by from the two medallions, and the sorcery should cost with X=4.

Are any other cards possibly affected by this bug ?
Atalya, Samite Master, Consume Spirit, Crimson Hellkite, Crypt Rats are the other cards in Manalink with restrictions on what can be spent on . Jet Medallion doesn't apply to any of them except Consume Spirit, of course, but there's Training Grounds and Dragonspeaker Shaman and plenty of other cards that do.

The calculation is correct in the program.

Since Drain Life can only use Black Mana as the X value, your jet medallion only has 1 generic mana in the spells cost to reduce.

Effectively to cast the spell for 4 damage you need 5 black sources

For drain life's purposes, think of X as a variable number of black mana symbols [(B)(B)(B)] (1) (B) for 3 damage or [(B)(B)(B)(B)] (1) (B) for 4 damage etc.

This also applies to your other examples, because they have mana restrictions "spend only [color] mana on X"

That's a common misconception, but it's false; see the rulings I linked. A cost reduction isn't a payment, so it isn't affected by restrictions on how you pay that cost. Relevant rules are 601.2b (X is chosen at proposal), 601.2f (total cost is modified by cost reductions), 601.2h (payment begins).

If I recall correctly, the way this worked changed shortly after Tempest was released specifically because of this issue; previously, Helm of Awakening had been ruled not to affect Drain Life's X cost.

Fixed for the majority of cards via "generic_spell" and for Drain Life / Consume Spirit via their specific functions.
Activated abilities shouldn't be a problem, as both Training Grounds and Power Artifact have the clause that they coulnd't reduce the activation cost to less than 1.

Atalya, Samite Master + Training Grounds no effect.

Drain Life / Consume Spirit + Jet Medallion - same bug. fixed
Plus, Drain Life and Consume Spirit don't do anything on resolution. fixed

Drain Life fixed in 5a5f172
Consume Spirit fixed in 0b6ee81
Interaction between both and cost reduction for spells fixed in 4ad10ae. This was a global bug and will fix all the other bugs like the interaction with additional costs.
I'll work on the same bug for activated abilities too.

Drain Life & Consume Spirit have been fixed.
Also they work correctly with cost reduction with Jet Medallion at least that I tested. They do deal correct amount of damage and gain life accordingly with 2 and 3 Jet Medallion in play. Only the X you see when you cast the spell is still wrong which if I remember correctly is hardcoded can't be fixed, right?

Edit: The other 2 I found that reduce cost of black spells, Stormscape Familiar and Thunderscape Familiar work also fine with Drain Life & Consume Spirit.