Summary and Info:
I created a package called libx11-xcb. It's the same as the libx11 package, except it is built without --without-xcb in it. The pkgbuild in reference is http://arch.nesl247.org/compiz-fusion/i686/libx11-xcb/PKGBUILD. I added the provides and conflicts, I just can't see the issue here. I hope it's not something I've overlooked.

Steps to Reproduce:

You can simply do pacman -S libx11-xcb, and hit yes to replace it when it says it conflicts. However when running pacman -S libx11 to go back, you get the following error:

nesl247@alex64 db $ pacman -S libx11
resolving dependencies... done.
looking for inter-conflicts...
:: libx11 conflicts with libx11-xcb. Remove libx11-xcb? [Y/n] y
done.
error: failed to prepare transaction (could not satisfy dependencies)
:: libx11-xcb requires dbus
:: libx11-xcb requires libxext
:: libx11-xcb requires libxfixes
:: libx11-xcb requires libxkbfile
:: libx11-xcb requires libxrender
:: libx11-xcb requires libxt
:: libx11-xcb requires lirc-utils
:: libx11-xcb requires rdesktop
:: libx11-xcb requires sdl
:: libx11-xcb requires startup-notification
:: libx11-xcb requires tk
:: libx11-xcb requires xorg-xinit