I was running the kernel-PAE-2.6.33-0.52.rc8.git6.fc13.i686 that came with the F13 alpha RC3 disc set.
Then I upgraded to the kernel-PAE-2.6.33-1.fc13.i686 from updates-test The first time I booted with that kernel and tried to start up the dialup networking it would not start. When I went into system->administration->network and looked at things and tried to re-create the dialup ppp connection it said this kernel does not support PPP. But now that I have rebooted again it suddenly all works.
I did put back the kernel-PAE-2.6.33-0.52.rc8.git6.fc13.i686 kernel from the install disc using rpm -ivh --force between the two bootups of kernel-PAE-2.6.33-1.fc13.i686 Guess I could remove the older kernel again and see if that breaks PPP again.