No X even though DISPLAY is working

[Per Starbäck]

In GNU Emacs 22.0.93.1 (i686-pc-linux-gnu)
 of 2007-02-08
configured using `configure  '--prefix=/home/per/emacs/pretest''

When starting emacs it started in the terminal and not with X as I
expected. (Starting emacs 21.3 works fine.) I see the entry

  ** If the environment variable DISPLAY specifies an unreachable X
  display, Emacs will now startup as if invoked with the
  --no-window-system option.

in the NEWS and assume that this check isn't working correctly.
My DISPLAY was set to ":0.0". I'm running Xorg 6.8.2 on CentOS 4.