I was just testing a bug I don't remember seeing covered elsewhere (human can activate computer's permanents abilities), and I see Chris just provided an answer to why
Furnace Spirit is different than all of the other red creatures I tested (it is hardcoded rather than use the keyword). In addition to being able to pump the computer's creatures (often to death in the case of the flowstone creatures such as
Flowstone Crusher), the human can activate
Pyrohemia and
Nevinyrral's Disk! You apparently can only activate the computer's permanents during your turn and only one activation at a time (unlike activating your permanents). I tested with practically all of the red pump creatures as well as
Uthden Troll (regeneration),
Enslaved Scout (mountainwalk), and
Viashino Grappler (trample). Yes, the human could just avoid activating the computer's permanents, so I'd say this is really pretty minor for now.
Also, the planeswalker combat damage error (creatures removed from combat still deal damage) has been fixed in 1/15 unofficial beta.
Korlash, Heir to Blackblade got its toughness bump from
Veteran Armorer, so that bug might be fixed (I haven't checked with Black Moon,
Glorious Anthem,
Giant Growth, etc., nor have I tested
Nightmare -- if nobody has reported on those by time I can get back to them, I'll test them out).
Reach of Branches is still inconsistent about returning to hand when you lay a
Forest, so that hasn't been fixed yet.
Control Magic effects still grant functional haste, since stolen creatures are not looked at as "not having been under current controller's control before the current turn."
AI problems I've run into include:
AI grants
Hooded Kavu fear twice.
AI often pumps creatures and then does not attack with them. Frequently, though, the creatures will become tapped without attacking.
AI occasionally will target {Null} with
Elvish Fury (with buyback), causing the
Elvish Fury to end up in the graveyard.
AI will not attack with a 1/4 creature when human only controls a 1/1 creature.
AI will attack with single non-vigilant creature when human controls an active
Royal Assassin.
New gameplay problem I've run into is that
Leaf-Crowned Elder's triggered ability is a "may" and you are not given the option to not, say, put a second
Doran, the Siege Tower into play. I also had several kinship creatures in play and you are really not given the option of what order to stack them (typically only matters if they include something like the
Leaf-Crowned Elder that might change what card is on top of your library).
Howling Mine does not play well with kinship creatures, even though the kinship ability should be activated during upkeep and
Howling Mine effect should take place during the draw phase. I suspect this is a problem because these aren't true phases in MTG Forge.