Innodb auto increment (no replies)

In what cases an auto increment ID in InnodDB table can be reset to 0 itself automatically?

I have an Integer Auto increment ID column in my InnoDB table and it does reset when I restart MySql server. Server version is 5.0.22. Is it a bug?

Is there any guarantee that the auto increment will never be dropped and each new ID will be calculated as max(ID) + 1?

Please answer my questions. Thanks in advance!