Fund check level are absolute but fund available can be a minus

Hi,
 
i have an charge of account (COA). the fund check level for that COA are absolute but when i do check the budget from Fund Available Inquiry, the amount in funds available column are minus. as far as i know, if the fund check level for a COA are absolute, the transaction can not proceed if the funds available are insufficient.
so it can be concluded that if the fund check level for a COA are absolute then funds available for that COA can not be a minus.
 
if i breakdown in fund available -> periode balance, there is Actual with Source are Cost Management and Category are Inventory.