Vue throws error Missing required prop even if provided

[sqal]

Vue.js version

1.0.26

Reproduction Link

vue@1.0.26 https://jsfiddle.net/84hvc9zh/
vue@2.0.0.rc-6 https://jsfiddle.net/84hvc9zh/1/

Steps to reproduce

Open reproduction links, check console

What is Expected?

Vue shouldn't warn about missing prop since it's provided via propsData.

What is actually happening?

Throws an error:

[Vue warn]: Missing required prop: <prop>
[Vue warn]: Invalid prop: type check failed for prop "<prop>". Expected String, got Undefined.

Happens only in Vue 1.x