For someone who knows the bug it's not a big deal, but we can't take that chance.
For those who didn't read it on TribalWar.com, the bug is this:
If you install the MP demo, then install the full game, then uninstall the MP demo (which you would do and makes sense), the uninstall on the MP demo whipes out your CD key information for the full game. Obviously this is a big problem and unfortunately something that we couldn't just patch out. Thus the delay. Hopefully it'll only mean an additional 24 hours.