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Describe the Bug:
I can't remember if we have met this again and my search didn't come with results,so:
I have Mindstatic in hand and untapped an Island,a forest, an Izzet Signet and a Simic Cluestone.AI casts a card and I don't get a chance to counter the spell.I know Izzet Signet cards can't be calculated correctly by engine but I don't know if a trick to give you the chance to use it with counterspells if it's mana is essential to cast the counterspell can be done.If you have one more mana available 4 without Izzet Signet then Mindstatic highlights and then you can use Izzet Signet just fine.

Which card did behave improperly ?
Izzet Signet

Which update are you using?(date,name)Which type(Duel,Gauntlet,Sealed Deck)
Manalink 2016/08/27: Eldritch Moon v2, duel

What exactly should be the correct behavior/interaction ?


Are any other cards possibly affected by this bug ?
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In a clean game I had an Underground Sea, a Mox Pearl and an Izzet Signet and I was able to Counterspell.

Signet declared mana production depends on the timestamp order of your mana sources: if you don't have available from mana sources with earlier timestamps than the signet, the signet won't claim that it can produce any mana. There isn't any way in the current mana-counting framework to make it wait for everything else to be counted first, so calling has_mana() or any of its variants inside a EVENT_COUNT_MANA is an error.

So besides the obvious bug that it should have checked for available in EVENT_COUNT_MANA and in EVENT_CAN_ACTIVATE instead of vice-versa, this is still a bad idea (and I'm pretty sure it was my bad idea) - it should just declare it has whenever it's untapped and not currently being activated.

Fixed in commit 1a063044.