landscape orientation differences between versions

[address@hidden]

Hello everybody

I'm working with Lilypond for several months now, and my experiments get
more and more realistic and interesting ;-) So I will follow up with
specific questions soon and hope someone may be able to give me advice.

As I'm new to this list, I would like to ask how I should handle the
following observation:

Let's start with the following code fragment:

{code}
\version "2.18.2"

\book {
  \paper {
    #(set-paper-size "a5" 'landscape)
  }
  \score {
    \new Staff
    <<
      { \relative c'{ c d e f}}
    >>
    \layout {
    }
  }
}
{code}

When I render this code with Lilypond v2.18.2, the PDF appears in
landscape view as expected - be it in Adobe Reader or in the Frescobaldi
score view.

When I render this code with Lilypnd v2.19.83, the PDF is rendered in
portrait orientation (and displayed so in the viewers mentionned).

When I change the version hint in the code to
{code}
\version "2.19.83"
{code}
and render the code with Lilypond v2.19.83, the PDF is rendered in
portrait orientation.

*Summary*
File version hint    Lilypond version   PDF orientation
2.18.2               2.18.2             landscape
2.18.2               2.19.83            portrait
2.19.83              2.19.83            portrait

Is this a bug? Where to post it? Or have I missed something?

Thanks in Advance
Steff