What about objects that has been removed from collection and parent is updated?

I execute this code:

document.lines.Add(new line(0,...))
document.lines.Add(new line(1,...))
document.lines.Add(new line(2,...))
document.lines.Add(new line(3,...))
session.saveOrUpdate(document);


later...

document.remove_line(line) -->
line.Document = null;
this.lines.remove(line);
session.SaveOrUpdate(document);

SQL generated-->
UPDATE DOCUMENT...
UPDATE LINE ... WHERE LINE = 0;
UPDATE LINE ... WHERE LINE = 1;
UPDATE LINE ... WHERE LINE = 3;
However line number 2 isn't deleted from database.

Mappings-->




What's wrong?
Thansk for all.

I don't think its wise to do this:
line.Document = null;
because document is part of the primary key of your line item. In my simple test case I get an exception if I set the parent element to null inside the transaction after removing it from the collection.