It is bugged in many ways and appears to simply not prevent ETB triggers from other cards occurring as it is supposed to.

Suspicious Stowaway entering the battlefield, or flipping has a chance to give MTGO an error and replay the entire game up to that point. Has happened 4 different times, all with different interactions with suspicious stowaway.
Notably: Playing and Transforming seem to cause the issue.

Aurelia, the Warleader triggers on her second attack resulting in 3 combats

Attempted to use Shigeki's Channel ability to retrieve X non-legendary cards from the graveyard on main phase, but was unable to while i had the appropriate mana to do so. I had used his first ability to put those cards into my graveyard with the intention to get them back.

chains glitches, just doesnt allow you to draw any cards and doesnt make you discard or mill

Conspicuous Snoop has all activated abilities of all cards on top of the library

Sylvan Library made the game restart and pass our turns to discard. We couldn't finish the game.

After attacking with Armored Skyhunter it seemed to cause two of my other creatures to disappear from the game. They didn't even end up in my graveyard or exile zones.

Round 1, Game 1: I controlled a Chandra, Torch of Defiance, and my opponent used Wild Slash to deal the Chandra lethal damage while controlling Etching of Kumano. I believe that the creature's ability, which is supposed to cause creatures dealt damage to be exiled, wrongly applied to my planeswalker. The Chandra was exiled, which caused me to not have enough cards in my graveyard to escape Kroxa, Titan of Death's Hunger, thereby affecting the outcome of the game.

I tried to use its ability during a slow and grindy match , mtgo was sluggish, but it sacced to itself. That is a bug, it should only allow to sacrifice another creature as i intended anyways.
So it sacrificed my creature that says , sacrifice "another" creature. Itself should not happen since its not a legal game process.

Karn the great creator, made my damping sphere a 1/1 instead of 2/2

Endless Loop caused by Either Tamiyo, Compleated Sage making a token of Garruk Relentless and Activating the 0 loyalty Ability that causes him to do damage to a creature and taking damage from that creature making an endless loop of Garruk Relentless trigger while the opponent is losing time on his timer or Garruk Relentless 0 Loyalty Ability can cause an endless loop.

Bug on dragon fire. normal 3 damage wasnt a option at all...

With Jinnie Fae and Felidar Retreat on the board, the second time the retreat triggers, the client will 'fail' to put the Landfall trigger on the stack, and never again. First time works, but not from second on. Two separate games this has happened.

Glorious Sunrise only lets you choose each mode once when it triggers. This is incorrect. You should be able to choose each mode more than once.

playing the new innistrad draft leagues i casted a storm the festival, i clicked my 2 choices of permanents and hit ok. upon resolution nothing came into play.

Fire // Ice targeted a Walking Ballista + Karn the Great Creator at 1 loyalty. Walking Ballista dying fizzled the Fire instead of the Fire still dealing 1 and killing Karn.

If Halo Fountain becomes a creature or a creature gains the activated abilities of Halo Fountain (e.g. Scheming Fence), you can activate the top-most ability by paying 1 Mana, tapping the Fountain (or the Fence), then untapping it again.

The problem here is that MTGO will only let me activate that ability if I have another already tapped creature on the battlefield.

I am unsure if this is a bug or working as intended, but, seeing as I can pay all the costs of the activated ability, I thought I should be able to activate it.