Issue with an extra fork layer or harmless?
Thanks for reporting that. I believe it should be harmless; on kernels above 3.5 we switched to having an intermediate process between Steam and the game to track the game's full process tree. I'll look into cleaning thew warning up.
Nothing extracted yet.
Seems since a while these warning are output (thanks @johndrinkwater for making the paste):
https://gist.github.com/johndrinkwater/0d4386fa1d9912f33b23
An easy way to see it is running a terminal as non steam game and attempting to autocomplete something from it. A lot of these warning will be shown, even if there aren't visible effects aside from the warning itself. The problem has appeared since around 1-2 months and is currently also in the stable version of steam.