lzma invoked incorrectly for mpfr port ?

[Joe VanAndel]

I'm running macports 1.70 on 10.5.6 (Intel).  I've just run sudo port
selfupdate.

When trying to install the "mpfr" port, macports seems to incorrectly
invoke 'lzma'.  (I have the current version, 4.63, provided by
macports).
port -d -v -f install mpfr reports:

DEBUG: Assembled command: 'cd
"/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_ports_devel_mpfr/work"
&& /opt/local/bin/lzma -dc
/opt/local/var/macports/distfiles/mpfr/2.4.0/mpfr-2.4.0.tar.lzma |
/usr/bin/gnutar --no-same-owner -xf -'

LZMA 4.63 : Igor Pavlov : Public domain : 2008-12-31

Error: Incorrect command

===============
As far as I can see, the correct command is:
/opt/local/bin/lzma d
/opt/local/var/macports/distfiles/mpfr/2.4.0/mpfr-2.4.0.tar.lzma -so |
/usr/bin/gnutar --no-same-owner -xf -

If I manually run lzma and gnutar to unpack the mpfr port, it builds fine.

Where is the the script that is invoking lzma incorrectly?