error in portupgrade

[Yuri X]

Good daytime!

I have a trouble using portupgrade/portinstall on FreeBSD 8.1. When I 
try to install some ports, especially with huge list of dependencies 
(e.g. kde4), the command fails with a Ruby exception. The listing is 
provided below. I have the most recent portupgrade 2.4.6, and my system is:

FreeBSD yntel 8.1-RELEASE FreeBSD 8.1-RELEASE #0: Mon Aug  2 16:24:27 
MSD 2010     yks at yntel:/home/src/src/sys/amd64/compile/KERNEL_20100802  
amd64

I also tried to "portinstall kde4" on other machines with e.g. FreeBSD 
8.0 or FreeBSD 8.1/i386, and it always resulted in the same exception. 
This also happens with different ports, I can not exactly remember which 
but there were a few, so it's likely not "kde4"-specific.

Thank you for your time,
Yuri.

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root at yntel ~># portinstall x11/kde4
--->  Session started at: Wed, 08 Sep 2010 23:30:48 +0400
[Gathering depends for x11/kde4 
..........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................--->  
Session ended at: Wed, 08 Sep 2010 23:31:01 +0400 (consumed 00:00:12)
/usr/local/lib/ruby/1.8/set.rb:263:in `merge': value must be enumerable 
(ArgumentError)
     from /usr/local/sbin/portinstall:879:in `get_all_depends'
     from /usr/local/lib/ruby/1.8/set.rb:195:in `each'
     from /usr/local/lib/ruby/1.8/set.rb:195:in `each_key'
     from /usr/local/lib/ruby/1.8/set.rb:195:in `each'
     from /usr/local/sbin/portinstall:878:in `get_all_depends'
     from /usr/local/sbin/portinstall:879:in `get_all_depends'
     from /usr/local/lib/ruby/1.8/set.rb:195:in `each'
     from /usr/local/lib/ruby/1.8/set.rb:195:in `each_key'
     from /usr/local/lib/ruby/1.8/set.rb:195:in `each'
     from /usr/local/sbin/portinstall:878:in `get_all_depends'
     from /usr/local/sbin/portinstall:879:in `get_all_depends'
     from /usr/local/lib/ruby/1.8/set.rb:195:in `each'
     from /usr/local/lib/ruby/1.8/set.rb:195:in `each_key'
     from /usr/local/lib/ruby/1.8/set.rb:195:in `each'
     from /usr/local/sbin/portinstall:878:in `get_all_depends'
     from /usr/local/sbin/portinstall:897:in `get_notinstalled_depends'
     from /usr/local/sbin/portinstall:777
     from /usr/local/sbin/portinstall:755:in `each'
     from /usr/local/sbin/portinstall:755
     from /usr/local/lib/ruby/1.8/optparse.rb:1310:in `call'
     from /usr/local/lib/ruby/1.8/optparse.rb:1310:in `parse_in_order'
     from /usr/local/lib/ruby/1.8/optparse.rb:1306:in `catch'
     from /usr/local/lib/ruby/1.8/optparse.rb:1306:in `parse_in_order'
     from /usr/local/lib/ruby/1.8/optparse.rb:1254:in `catch'
     from /usr/local/lib/ruby/1.8/optparse.rb:1254:in `parse_in_order'
     from /usr/local/lib/ruby/1.8/optparse.rb:1248:in `order!'
     from /usr/local/lib/ruby/1.8/optparse.rb:1241:in `order'
     from /usr/local/sbin/portinstall:565:in `main'
     from /usr/local/lib/ruby/1.8/optparse.rb:791:in `initialize'
     from /usr/local/sbin/portinstall:229:in `new'
     from /usr/local/sbin/portinstall:229:in `main'
     from /usr/local/sbin/portinstall:2213
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