[wp-hackers] Will upgrading 1.2 DB to 1.3 break it for 1.2?

[Arthur Jennings]

AFAIK It depends what you mean. If you upgrade your existing entries
to 1.3 you can't "downgrade" them back to 1.2 -- you'd have to restore
from a backup. Nor can you run two different versions of WordPress
with the same set of entries.

-- 
Arthur Jennings
http://www.timeistight.com