Envelope DL insert adds 5cm top margin

When I select Insert Envelope, I select the DL envelope. This is correctly sized at 22cm by 11 cm. The offset for addressee (5.5cm) and sender (1cm) are correct as is the envelope preview on the envelope dialog.

However, when I click New Document (or Insert) I get an envelope with a 5cm margin added at the top. The “envelope” page has been created with a page height of 16cm, not the 11cm specified in the Envelope dialog. The text boxes for addressee and sender have been moved down 5cm, so if I remove the 5cm top margin in the Page Style : Envelope dialog and resize the page to 22 x 11cm the text boxes then have to be both moved up by 5cm.

I cannot see any possible use to having LO add a 5cm top margin to the envelope, so is there some preference parameter available to stop this behaviour?

For the moment (since LO v5) I am using a DL envelope template for all my letters, but it seems somewhat pointless to have an Insert Envelope option that does not work.

The same thing happens if I default my Canon or Epson printers, so I don’t think it is related to the printer. I also thought it may have been to centre an envelope on an A4 sheet for printers that do not understand page sizes, but that would have required a 5.5cm offset (11cm/2).