+1 for Revathi's answer, it's almost certainly the support process Setup > Customize > Cases > Support Processes
Create a support process and then create a record type
The support processes are there for Cases, Opportunities, and Leads specifically because they treat the picklist values as an ordered list. This way when you run reports and dashboards, specifically funnel charts, the values come back in the specified order.
Processes respectively..
Reference: https://help.salesforce.com/HTViewHelpDoc?id=customize_recordtype.htm&language=en_US
Setup > Customize > Cases > Support Processes
Create a support process and then create a record type
The support processes are there for Cases, Opportunities, and Leads specifically because they treat the picklist values as an ordered list. This way when you run reports and dashboards, specifically funnel charts, the values come back in the specified order.