The help states that you should: “Enter the amount of space to leave between the left edge of the page and the left edge of the header.” The same for the right margin. What is actually happening is that the header margin is added on to the page margin. It should be possible to have a header that is wider than the page margin.
1. New Text Document.
2. Format → Page and set margins to 2 cm.
3. Switch to Header tab.
4. Set Header On.
5. Set Left Margin to 1.00 cm and OK.
Header left margin is 1.00 cm (from left edge of page).
Header left margin is 3.00 cm (from left edge of page).
A negative number cannot be entered.
If this a bug and the header and footer margins are made to take into account the page edge then the default settings for them should be the page margins. So if the left page margin is 2.00 cm then the header right margin should say 2.00 cm. There would also be the issue of backwards compatibility.
If this is not a bug then the help should be updated to say that the header cannot be wider than the page margins or that it is in addition to the page margins.
There are workarounds such as changing the indents of the paragraph.
Windows Vista 64
Build ID: 88805f81e9fe61362df02b9941de8e38a9b5fd16
I agree there is an inconsistency. I suppose that the help should be updated as the header margin is meant from the page margin and not the page edge (you can also see it in the small preview).
(In reply to A (Andy) from comment #1)
> I agree there is an inconsistency. I suppose that the help should be
> updated as the header margin is meant from the page margin and not the page
> edge (you can also see it in the small preview).
Yep, good idea. See bug 99739
Setting this issue as enhancement.