undefined method AFTER First load

I have a fairly simple model to which i've added a method:

def pro?
     return true
end

For some reason myModel.pro? works just fine the First time i call it.
But when i reload the page i get an undefined method error.

The symptoms are very similar to
http://dev.rubyonrails.org/ticket/3930

except that it's a normal model that's not importing anything funky
and is in the standard models folder.

Has anyone else seen this?

I've got an older version of the codebase that doesn't have this
problem when run under the same conditions, so obviously it's not
rails itself but something I've borked... I'm just at a bit of a loss
as to what.

I've tried it with rails 1.2.2, 1.2.3 and edge all under mongrel with
ruby 1.8.5 on ubuntu edgy.

For future people the problem seems to be that when i import a module
into my controller custom methods go missing on my models. I have no
solution for this yet.