Error message V50R 024 when creating delivery via VL10C

Hi ,

I am facing one strange lock issue.

User is trying to create delivery for sales order containing more than 1200 items va tcode vl10c.

It showing information message V50R 024

"At least one order was blocked and could not be delivered".

When we check sm12 we found that it showing salesorder is locked by same user.

By manually deleting lock it able to proceed to creation of delivery.

User has never opened sales order when running TCODE vl10c.

Is there any chance that lock happened beacuse of some bug in sap programme when creating delivery for large sales order.

Any suggestions / solutions appreciated.

Thanks in advance

Manoj