[gentoo-user] problems emerging some ruby packages

[Jack]

I'm helping support a web site hosted at Heroku and written in Ruby on  
Rails.  Following some tool upgrades there, I upgraded my local rails  
to 3.1, uninstalling the previous version 2.7.  I  now have  
RUBY_TARGETS="ruby31" in make.conf. and several specific dev-ruby  
package versions in package.accept_keywords.  Most of them upgraded  
fine, or at least reinstalled (using a version supporting ruby31 after  
unmerging the old version) but some are giving me grief.

For example, "emerge -1 dev-ruby/thor" gives me

!!! Problem resolving dependencies for dev-ruby/thor
... done!

!!! The ebuild selected to satisfy "dev-ruby/thor" has unmet  
requirements.
- dev-ruby/thor-1.2.1::gentoo USE="-doc -test" ABI_X86="(64)"  
RUBY_TARGETS="-ruby27 (-ruby30) (-ruby31)"

   The following REQUIRED_USE flag constraints are unsatisfied:
     any-of ( ruby_targets_ruby27 ruby_targets_ruby30  
ruby_targets_ruby31 )

I would expect USE_RUBY="ruby31" to translate into ruby_targets_ruby31,  
but even explicitly adding that to package.use has no effect.  Is there  
something I'm missing turning off ruby31, specifically for just a small  
number of packages?  (so far the only other one with this problem is  
dev-ruby/mini_mime).

Portage has two versions of thor: 1.1.0 and 1.1.2, both marked stable  
for amd64, and 1.2.1 has USE_RUBY="ruby26 ruby27 ruby30 ruby31" so I  
don't see any reason it's not working.

I already have railties installed (using -O) with ruby31, and it  
depends on thor via ruby_add_redepend, which I read as requiring thor  
with ruby31.  thor is not mentioned in any file under /etc/portage.

Does anybody see what I'm missing?

Jack