SQL server identity column values start at 0 instead of 1

I've got a strange situation with some tables in my database starting its IDs from 0, even though TABLE CREATE has IDENTITY(1,1). This is so for some tables, but not for others. It has worked until today.

I've tried resetting identity column:

DBCC CHECKIDENT (SyncSession, reseed, 0);

But new records start with 0. I have tried doing this for all tables, but some still start from 0 and some from 1.

Any pointers?

(i'm using SQL Server Express 2005 with Advanced Services)