I've pretty much stopped using Sheeva because doing her 2, 1, 2, F1 causes desync.
Barakas 2, 2, 2+1, causes desyncs (for me anyways).
I'm astounded that this due to custom button mapping. I mean the default button layout for this game is retarded. This isn't Street Fighter, it's MK. Punches have always been vertical layout, not horizontal.
Regardless, it's ridiculous that simply choosing to have custom buttons means you run the risk of desyncs online. As this doesn't always happen, I don't know if two players with custom button layouts are safe to play each other, as I would assume the majority just play with the default controls. Last night, I had desyncs galore, all in the middle of combos.
And yes, Desyncs can still occur by simply pressing start on your character icon. It's like the game saves you the trouble of picking an alt, and then desyncing...it just desyncs from the moment you press start.
Desync, Ed Boons ultimate fatality.