\includepdf and \includepdfmerge behave differently reg. doublepages option

Binary package hint: texlive-base

From the manual: "The \includepdfmerge command uses the same options as \includepdf". It doesn't mention there to be differences in the semantics. However, the commands behave differently as can be seen in the attached PDFs.

$ cat a-includepdf.tex
\batchmode
\documentclass[a4paper,landscape]{article}
\usepackage[utf8]{inputenc}
\usepackage{pdfpages}

\begin{document}
\includepdf[pages=-,nup=2x1,doublepages=true,frame=false]{source-1.pdf}
\end{document}
$ cat a-includepdfmerge.tex
\batchmode
\documentclass[a4paper,landscape]{article}
\usepackage[utf8]{inputenc}
\usepackage{pdfpages}

\begin{document}
\includepdfmerge[,nup=2x1,doublepages=true,frame=false]{source-1.pdf,-}
\end{document}
$

The generated PDFs are attached.
They look different. However, I would have expected them to look the same.

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: texlive-latex-recommended 2009-10
ProcVersionSignature: Ubuntu 2.6.38-2.29-generic 2.6.38-rc3
Uname: Linux 2.6.38-2-generic x86_64
Architecture: amd64
Date: Wed Mar 9 17:21:30 2011
PackageArchitecture: all
SourcePackage: texlive-base