After changing default values in tables Autoincrement starts at 0

I'm sorry
i changed the table definition by using the GUI in 3.1.1 on WinXp.
Courios is, that the made changes by default values not exist after 
saving and reopening anymore.

But the Autoincrement from my primary Key in this table begins after 
that at 0 again. The inserted data is not count straight up. I 
should have deleted the id 0 before.

After changing the table definition i could insert exact 1 dataset 
with ID 0. After that i can't insert datasets anymore.

Is this a known bug, or what can i do now, because i use the indexes 
in other tables too.

Ulf