defect: qca-2.0.0 missing -L/opt/local/lib when building examples?

[rechner@…]

When I tried to install kdegraphics4 the building of qca failed:

--->  Building qca
Error: Target org.macports.build returned: shell command " cd "/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_ports_devel_qca/work/qca-2.0.0" && make all " returned error 2
Command output: /opt/local/libexec/qt4-mac/bin/uic keyselect.ui -o ui_keyselect.h
/opt/local/libexec/qt4-mac/bin/uic mainwin.ui -o ui_mainwin.h

[snip]

/usr/bin/g++-4.0 -headerpad_max_install_names -arch ppc -o cmssigner.app/Contents/MacOS/cmssigner pkcs11configdlg.o prompter.o certviewdlg.o keyselectdlg.o certitem.o main.o moc_prompter.o moc_certviewdlg.o moc_keyselectdlg.o moc_certitem.o qrc_cmssigner.o   -F/opt/local/libexec/qt4-mac/lib -L/opt/local/libexec/qt4-mac/lib -L../../lib -lqca -framework QtGui -L/opt/local/libexec/qt4-mac/lib -F/opt/local/libexec/qt4-mac/lib -framework Carbon -framework AppKit -lpng -framework QtCore -lz -lm -framework ApplicationServices
ld: library not found for -lpng
collect2: ld returned 1 exit status
make[2]: *** [cmssigner.app/Contents/MacOS/cmssigner] Error 1
make[1]: *** [sub-cmssigner-all] Error 2
make: *** [sub-examples-all] Error 2

Error: The following dependencies failed to build: kdegraphics4 qca
Error: Status 1 encountered during processing.

So I went to the build directory

/opt/local/var/macports/sources/rsync.macports.org/release/ports/devel/qca/work/qca-2.0.0/examples

and called the long last command with an added "-L/opt/local/lib" as the first option to "g++-4.0". After that "port install qca" completed without problems.

By the way: "-I/opt/local/lib" is in my "CFLAGS" environment and many other ports compiled without problems. But I don't know much about compiling C programs, maybe I'm on the wrong track here...