bug in Guided Access

when using Guided Access, there's an option to circle on the screen where you would like to disable.

but in the App Phone , I found that diabled area is still touchable :

after dialing a number, touch the "contacts" icon to bring out All contacts, and then all disabled area is touchable! and I think it's a bug.

it's ios 8.3 on ip6

hope someone understand me