In LO Writer, with Web Layout mode selected, New Window is disabled. New Window works fine in Print Layout. This appears to be by design, but I can't figure out why, nor can I find any documentation to this effect. I say I think it's by design because selecting Web Layout closes any duplicate windows. If it was a mere bug, I would have expected a crash instead. :^)
reproducible with LO 4.0.1.2 (Win7 Home, 64bit) I can not explain to me any reasons for a disabled NEW WINDOW in the WEB LAYOUT view. In my opinion this is a bug.
*** This bug has been marked as a duplicate of bug 60129 ***