This is somewhat critical. It breaks the functionality of printing any page in an other size then by iso-formats. 
When you make a new writer document and set for example the wide of the page from A4 (210mm) to lets say 200mm and confirm that, your page get visable smaller (reducing seems to work). But when you then press print, you get wide of 210mm instead of 200m at the print preview. When you print the page, libreoffice send 210mm wide document to the printer. Not a 200mm wide page as you have set before.

Win 7, 64bit, LibreOfficeDev_5.0.0.0.beta1_Win_x64.msi