I tried to search for a similar issue but I could find none.

I'm using the OptionsResolver as a component in a package I'm writing.

In 2.6, the OptionsResolver class still implements the OptionsResolverInterface interface.
So if the interface is auto-loaded by default the trigger_error() call in the OptionsResolverInterface.php is executed. And I get the following error: The "Symfony\Component\OptionsResolver\OptionsResolverInterface" interface was deprecated in version 2.6 and will be removed in 3.0. Use "Symfony\Component\OptionsResolver\OptionsResolver" instead.

Am I forgetting something?