Event issue when inserting additional saleslines using code

Hi,

i have a small issue regarding events. I'm inserting additional saleslines using event onModify. For example, when the line is modified several lines is added. That part works correct. But the issue is when posting. When i specify amount on "qty to-ship" and post it as "shipping", the "quantity shipped" field on salesline becomes empty afterwards. Hope the issue is understandable.