Multiple module installations

[Christoph Deil]

Hi,

listing my installed modules shows that some packages are installed multiple times:

$ port list installed
[...]
py26-tz                        @2010b          python/py26-tz
py26-tz                        @2010b          python/py26-tz
python25                       @2.5.5          lang/python25
python25                       @2.5.5          lang/python25
python26                       @2.6.4          lang/python26
python_select                  @0.3            sysutils/python_select
qhull                          @2010.1         math/qhull
qrupdate                       @1.0.1          math/qrupdate
qt4-mac                        @4.6.2          aqua/qt4-mac
qt4-mac                        @4.6.2          aqua/qt4-mac
qt4-mac                        @4.6.2          aqua/qt4-mac
qt4-mac                        @4.6.2          aqua/qt4-mac
rarian                         @0.8.1          textproc/rarian
readline                       @6.1.000        devel/readline
root                           @5.26.00        science/root
root                           @5.26.00        science/root
[...]

I noticed that everytime I do a port selfupdate, qt4-mac is installed anew, which takes hours.
Since the version number is always identical this seems unnecessary.

Are these multiple module installations by macports normal / necessary?
Should I delete the multiple older installations?
How do I select which ones to delete?

Thanks, Christoph