I mistakenly added 6 Hallowed Fountains to a Standard deck and it wasn't flagged as being invalid for Standard. This also appears to be a problem with the other shocklands from Return to Ravnica. The M13/Innistrad dual lands were correctly flagged if I put more than four of them.

I wonder if it is due to them being true dual lands (e.g., swamp forest). Perhaps the system is counting them as a basic land subtype, rather than as unique lands.

The issue here is that actually the system only counts the total cards in a deck in order to validate it or not. A deck having between 60 and 70 cards or exactly 100 cards will be marked as valid. There is no actual check for individual cards and their number in the deck. This is of course a limitation in the system and it will be addressed in the future.

Thanks for the patience and for reporting the issue :)

Laura, decks larger than 70 (or even 100!) cards are legal for sanctioned MTG play. When you guys get around to tweaking those screens, that logic should be updated, too.

:) The new software version indeed apparently does not check for "more than 4 of" in a deck. The *old* software did, which is why I mentioned this particular discrepancy. In theory you can close this bug out as it refers to a feature not currently available. :)

Preppy wrote::) The new software version indeed apparently does not check for "more than 4 of" in a deck. The *old* software did, which is why I mentioned this particular discrepancy.

Nope, we never had any smart checks for validity. We only check the number of cards and the fact that the cards are legal in that specific format.

Just for proof, I've taken a screenshot of a new deck I made using the old version :P

Right, but that's a shock land, which is what I was mentioning had never been checked for >4-ness. I had thought that if you had put 6 Thragtusks or 6 Clifftop Retreats in a deck you got warned that >4 wasn't valid. Perhaps I was mistaken. But regardless this feature isn't implemented, so it's a feature request masquerading as a bug at this point. My bad. :)

No worries. The feature's on the list of things to be done, just not at the very top. So... soon (TM) :D