Thanks for suggesting looking at texmf.cnf
I've found the following: TEXMFMAIN = /usr/share/texmf TEXMFCONFIG = $TEXMFMAIN
% - make sure that $TEXMFVAR precedes $TEXMFMAIN in the TEXMF definition.
TEXMF = {!!$TEXMFCONFIG,!!$TEXMFVAR,!!$TEXMFMAIN,$TEXMFHOME,!!$TEXMFLOCAL,!!$TEXMFDIST}
As you can see TEXMFCONFIG is equal to TEXMFMAIN, so TEXMFVAR is not before TEXMFCONFIG. So changing the line to
TEXMF = {!!$TEXMFVAR,!!$TEXMFCONFIG,!!$TEXMFMAIN,$TEXMFHOME,!!$TEXMFLOCAL,!!$TEXMFDIST}
solves the problem.
Bert