Disable first boot.
It seems to me that your problem has more to do with the first boot thing.
Can you tell me how your FC starts booting? For example, it happened in my case that as the computer went into fedora core, it started off with a 1280x1024@60 screen, but as soon as the login screen was about to load, my system jumped to a 800x600 screen.
If its the same case with you, just do this: System>Administration>Server Settings>Services. Once there, look for firstboot, uncheck it, and then stop it. Then, click on save. Similarly, switch to all runlevels and save it until done.
That should solve your problem.