I jsut logged in here to report the same problem and was surprised that the thread is already exist.
Given that this "untargetability" is unique to the game (although similar to stealthed targets), it's certainly possible that there are unintended bugs in how it functions. That's why these reports are great!
The difference between stealth and outmanuever, from what I can tell, is that the definition of Stealth, at least from the list on Gaming Fans, is that the "Character can not be targeted directly", whereas, Outmanuever excludes the word "directly" and just says cannot be targeted. To me, this implies that HMF, as long as it has the outmanuever buff, cannot be the target from any type of attack, whether it is direct, indirect, random, etc. Outmanuever is basically an upgraded stealth ability. At least that is how I am interpreting it with respect to otehr definititions in game.
Opinions will vary, especially between HMF and Spy users. I am an HMF user (full disclosure), but I am trying to look at this unbiasly, through other game definitions and interactions. Really interested to see if we get an official response on this and what it is.
