From Bugzilla Helper:
User-Agent: Mozilla/5.0 Galeon/1.2.7 (X11; Linux i686; U;) Gecko/20030131

Description of problem:
Anytime I change a value that causes the
/tftpboot/linux-install/pxelinux.cfg/default to be rewritten, a new
copy is appended to the old one.  The new copy should replace the old
copy.

It appears to me, that the problem is in the pxeOSList.saveOSList
method in pxeos.py.  The line 

defaultFD=open("%s/pxelinux.cfg/default" % PXEBOOTDIR, "a")

should be

defaultFD=open("%s/pxelinux.cfg/default" % PXEBOOTDIR, "w")
                                                       -^-


Version-Release number of selected component (if applicable):
redhat-config-netboot-0.1.1-19

How reproducible:
Always

Steps to Reproduce:
1. Select Configure -> Network Installation from the menu of the
redhat-config-netboot window.
2. Click the close button
3. Check the /tftboot/linux-install/pxelinux.cfg/default file
4. Repeat


Additional info: