[itsm] Question on Ticket Numbering

We have our ticket numbering set to auto increment, we started with a 5 digit ticket number to a 6 digit to now a 7 digit in a really short time. (10 thousand tickets though it appears as though 1 million) This is what happens: First ticket- 10001, 10002, and so on until it reaches 10999 then switches to 101000, instead of going to 11000. It just adds another place value. Now it went from 109999 to 1010000 Any idea as to why it may be doing this? In just 4 months we have gone from a 5 digit number to a 7. We really don't want to have 11 digit ticket number by the end of the year mark.