Inheritance problem: failing spec (why?)

```
CarrierWave::Uploader.version shouldn't raise an error in this test
Failure/Error: @instance.image = stub_file('test.jpg')
NoMethodError: undefined method `foo' for #<#<Class:0x00000005a86da8>:0x00000005b4f190>
# ./lib/carrierwave/uploader/processing.rb:84:in `block in process!'
# ./lib/carrierwave/uploader/processing.rb:76:in `each'
# ./lib/carrierwave/uploader/processing.rb:76:in `process!'
# ./lib/carrierwave/uploader/callbacks.rb:16:in `block in with_callbacks'
# ./lib/carrierwave/uploader/callbacks.rb:16:in `each'
# ./lib/carrierwave/uploader/callbacks.rb:16:in `with_callbacks'
# ./lib/carrierwave/uploader/cache.rb:129:in `cache!'
# ./lib/carrierwave/uploader/versions.rb:263:in `block in cache_versions!'
# ./lib/carrierwave/uploader/versions.rb:261:in `each'
# ./lib/carrierwave/uploader/versions.rb:261:in `cache_versions!'
# ./lib/carrierwave/uploader/callbacks.rb:18:in `block in with_callbacks'
# ./lib/carrierwave/uploader/callbacks.rb:18:in `each'
# ./lib/carrierwave/uploader/callbacks.rb:18:in `with_callbacks'
# ./lib/carrierwave/uploader/cache.rb:129:in `cache!'
# ./lib/carrierwave/mount.rb:329:in `cache'
# ./lib/carrierwave/mount.rb:163:in `image='
# ./lib/carrierwave/mount.rb:148:in `image='
# ./spec/uploader/versions_spec.rb:183:in `block (3 levels) in <top (required)>'
```