Class reloading breaks type-checking

class-reloading.rb

class Foo
end

Foo.object_id                   # => 34581480

f = Foo.new                     # => #<Foo:0x000000041f53c0>

f.class.object_id               # => 34581480

# This just prevents the "const redefined" warning
Object.send(:remove_const, :Foo)

# "Reload" class Foo
class Foo
end

Foo.object_id                   # => 34580180
f.class.object_id               # => 34581480

f.is_a?(Foo)                    # => false
f.class == Foo                  # => false
f.class.name == "Foo"           # => true

The conversation this was part of was discussing Rails autoloading in development mode. It's not clear to newbs (until it's explained in an example like this) that the autoloading mechanism works this way.