Curious SQL Server Bug

I’ve encountered what appears to be an odd bug in SQL Server 2000: when exporting/importing data, it appears to make edutcated guesses about what the values in a bigInt column should be in the new table. Case in point? A list of IDs, wherein the first 150 or so were roughly in order (with a few skips and jumps). Then, a jump of 2 000 000 and then some more. However, the imported data doesn’t make that jump of 2 000 000, it simply goes up in order, like an identity, at that 151st record. I’ve no idea why. It’s not a primary key, I’ve tried it with and without an index on the column, but all the same. It’s too big to be an Int, so I can’t do that. Changing it to a Float removed the issue, but I’d like to understand why this is happening at all. And why specifically to bigInts?