I just saw a Mycelium wallet misbehave heavily: a transaction was shown as sending only the fee, not the rest. However, on the block chain, it was sent. Mycelium balance was then out of sync with the block chain.
Didn't happen on my device, so I don't have more details right now. But naturally I'm suspecting mutated transactions to be involved.
Erm, somewhat bad timing with this whole bitcoin-wide attack thing. The guys may be on their way to Berlin as we speak, so probably won't get a chance to look at things till later. I asked them for feedback on whether Mycelium is affected by this thing. Will let you know soon as I hear back.