Sorbet weird $global type behavior

Gemfile

gem 'sorbet', :group => :development
gem 'sorbet-runtime'

main.rb

# typed: true
require "sorbet-runtime"
require "./rollout_setup"

extend T::Sig

T.reveal_type($rollout) # => T.untyped (incorrect)

sig { params(val: Rollout).returns(Rollout) }
def expects_rollout(val)
  val
end

expects_rollout($rollout) # no error (as expected)
expects_rollout("not a Rollout") # error (as expected)

$rollout = 123 # no error (not expected)

rollout_setup.rb

# typed: true
require "sorbet-runtime"

class Rollout; end

$rollout = T.let(Rollout.new, Rollout)

srb_tc_output.txt

main.rb:7: Revealed type: `T.untyped` https://srb.help/7014
     7 |T.reveal_type($rollout) # => T.untyped (incorrect)
        ^^^^^^^^^^^^^^^^^^^^^^^
  From:

main.rb:15: Expected `Rollout` but found `String("not a Rollout")` for argument `val` https://srb.help/7002
    15 |expects_rollout("not a Rollout") # error (as expected)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    main.rb:9: Method `Object#expects_rollout` has specified `val` as `Rollout`
     9 |sig { params(val: Rollout).returns(Rollout) }
                     ^^^
  Got String("not a Rollout") originating from:
    main.rb:15:
    15 |expects_rollout("not a Rollout") # error (as expected)
                        ^^^^^^^^^^^^^^^
Errors: 2