Created simple gist to show this https://gist.github.com/tarlepp/be57391ceead9099d66e3500001ae58b also tested with phpunit 5.7.11 and the results are the same.

I tracked this to commit e59f0e0#diff-0e793081ceb720201745c982a568903fL1046

Maybe that $container->setAlias('annotation_reader', 'annotations.cached_reader'); was removed by mistake ?