Move to AR 3.2.1, now thread behaves differently

I have this piece of code below. It used to work fine, I was using
active record 2.3.8. I upgraded to
active record 3.2.1 and moved some gems into a gemfile. Now what
happens is rec below is an active record instance, when I enter the
thread it appears to become nil. The method repopulate() is not longer
defined. Why would that happen ?

def new_thread(slot,&block)
th =
@pool[slot] = th

p rec.respond_to?(:repopulate) # this is fine
@tpool.new_thread(slot) do # see method definition above
Thread.current[:rset_fact] = model
puts ‘in thread’
p rec.respond_to?(:repopulate) # no longer defined
rec.repopulate # error rec is nil