On both of my linux systems, Alpha PC164 and Pentium II-MMX 300, running Mach64 X server, linuxconf issues a bunch of Gtk widget errors immediately aftering selecting any field to inspect/modify. It appears to continue to function normally vis a vis actually controlling the selections made.
Upgrading to the latest gtk+ as well should fix this.
If the upgrade does not fix it, please re-open this bug to let us know, and install the latest gnome-linuxconf from RawHide or Lorax which has code in it to work around this bug.