portupgrade problems on 4.x

[Jake Lloyd]

portupgrade on my two 4.x boxes seems to have gone wrong, starting just 
today. The last successful of run of portupgrade (on only one of those 
systems) was to upgrade thunderbird on 14.07.2005. But today
#portupgrade <any-port>
outputs the following:

[Failed `Inappropriate file type or format'] [Updating the portsdb 
<format:bdb1_btree> in /usr/ports ... - 13190 port entries found 
.........1000.........2000.........3000.........4000.........5000.........6000.........7000.........8000.........9000.........10000.........11000........./usr/local/lib/ruby/site_ruby/1.8/portsdb.rb:613: 
[BUG] Segmentation fault
ruby 1.8.2 (2004-12-25) [i386-freebsd4]

Abort (core dumped)

and, indeed, there is a ruby18.core file of some 10 Mb.
Naturally, the <any-port> is not upgraded.

Most mystifying is, there has been change neither to any ruby ports nor 
to portupgrade itself, since the most recent uses of the portupgrade.

Output from relevant pkg_info is as follows:

# pkg_info | grep ruby
ruby-1.6.8.2004.07.28_1 An object-oriented interpreted scripting language
ruby-1.8.2_4        An object-oriented interpreted scripting language
ruby18-bdb1-0.2.2   Ruby interface to Berkeley DB revision 1.8x with 
full featu
ruby18-programmingruby-0.4 The source of the Programming Ruby 
("pick-axe") book in XML

# pkg_info | grep portupgrade
portupgrade-20041226_5 FreeBSD ports/packages administration and 
management tool s

(ruby-1.6 is on only one system; some cruft i haven't taken time to 
clean out, but it hasn't caused any problem, so don't think that's related)

This problem does *not* appear today on my 5.x system.

Thanks for any help, advice.

- Jake