Page number restarts unexpectedly

running openjade on following sample with stock 1.77
stylesheets, no jadetex.cfg
-----------------------------------------------
<book>
<title>test</title>
<preface>
<title>Preface title</title>
<para>Preface paragraph blabla.</para>
</preface>
<chapter>
<title>First Chapter</title>
<para>blabla</para>
</chapter>
<part>
<title>First Part</title>
<chapter>
<title>Second Chapter</title>
<para>blabla</para>
</chapter>
</part>
</book>
-----------------------------------------------
gives the following page sequence:
--------------------------
[blank] (Title page)
[blank]
iii (TOC)
i (Preface)
1 (First Chapter)
[blank] (Part I)
2 (Second Chapter)
--------------------------
This sample highlight two problems:
1) "Preface" first page should be numbered "iv" or "1"
but not "i", which is quite confusing after "iii".
2) last page should be numbered "3" (For larger first
chapters, the first page of second chapter is always "2")