Conflict with /Applications/MacPorts when multiple MacPorts instances installed

[J. Lewis Muir]

Activating python25 in a second MacPorts instance fails for me when my
first instance already contains an activated python25.

According to

  http://guide.macports.org/#installing.macports.source.multiple

I can install more than one MacPorts instance on the same host.
However, when I do this and then install bzr which installs python25 in
a second instance, I eventually get the following error output:

--------------------
--->  Fetching python25
--->  Attempting to fetch Python-2.5.2.tgz from http://www.python.org//f
tp/python/2.5.2/
--->  Verifying checksum(s) for python25
--->  Extracting python25
--->  Applying patches to python25
--->  Configuring python25
--->  Building python25 with target all libpython2.5.dylib
--->  Staging python25 into destroot
--->  Installing python25 2.5.2_5+darwin_9
--->  Activating python25 2.5.2_5+darwin_9
Error: Target org.macports.activate returned: Image error: /Applications
/MacPorts/MacPython 2.5/Build Applet.app/Contents/Info.plist already exi
sts and does not belong to a registered port.  Unable to activate port p
ython25.
Error: The following dependencies failed to build: py25-bz2 python25 py2
5-crypto py25-curl curl pkgconfig zlib py25-docutils py25-hashlib openss
l py25-paramiko py25-socket-ssl py25-zlib
Error: Status 1 encountered during processing.
--------------------

Is there a way around this?  Perhaps another configure option, similar
to the --with-tclpackage option, such as --with-apppackage is needed?  I
could then configure my development MacPorts install with something like

  ./configure
    --prefix=/opt-dev
    --with-tclpackage=/Library/Tcl/macports-dev
    --with-apppackage=/Applications/MacPortsDev

Of course, I can work around this by moving /Applications/MacPorts out
of the way while I work with my development instance, but it would be
nice if I didn't have to do that.

Or maybe I'm not understanding something correctly.

Thanks,

Lewis