This is curious but probably a known issue. Or, it is me.

 From:  Michael Gibson
5051.5 In reply to 5051.4 
Hi Leonard,

> Are you saying the history function, because I moved the
> plane, assumes that I do not want the curves therefore,
> they are to disappear or be deleted?

Only if you move it in such a way that the projection actually misses the plane and so does not produce any output objects at all.

If you do that it is the equivalent of deleting the objects.

- Michael