production order no skipping

Dear PP Guru,s,

Production order no is skipping in between the range. i checked in the CO82 for no range and current no. staus. when i see in COOIS in between some no are skipping and this No. range is not assigned to any other order type. this is internal no. assignement. can any one tell me about this what could be the reason for this? helpful answer will be rewareded.

Regards,

sree