Actium, you are my hero :). This hopefully should work until BI fixes it.
May 10 2016
Installing all those dependencies is not an option - a display server on a linux root server is, mildly said, rubbish and installing two network managers at once has the potential to cause serious problems.
The steamclient.so seems to have new shared libaries as a dependency, including X11, OpenAL, pulse, and the GNOME network manager... which is pretty crap for a linux dedicated server and shouldn't be necessary at all.
We have tons of these on our server. They don't seem to be mission related, maybe mod related or script related.... I somewhere read that it is a debug message for setpos. They even happen on vanilla missions, though they are very rare there. If you can't reproduce them on your server, you can investigate them on our server if you want, just sent me a PM/E-Mail or skype me (I'm in the skype chat from Dwarden).