I got the same problem with my new SteelSeries Nimbus, I bought yesterday only to play Minecraft on my iPad Air and iPhone 6S Plus. I am not able to use the left and right analog sticks at the same time. You can't believe the disappointment I have about this dumb bug. Every other game works well. Mojang isn't able to develop ground features with MFi? What is this? Even because they got the API of MFi! They don't have to develop an own controller feature. Just to figure out how the API works correct. Hope they bring an update soon.
Fixed in 0.14.0 on my iPad Air 1.