Bad redirect after fill communication preferences form

Created by: marcineqpol

Hello. When I add an absolute address, which is to be redirected after completing the form - it redirects to the address like insert only of the subpage like: http://darmowe.westus2.cloudapp.azure.com/demo/http://www.staroflife.pl.

I tryied to recreate this issue on D7.59, Civi 5.2alpha and D7.59, Civi 5.1. My demo page with this issue: http://darmowe.westus2.cloudapp.azure.com/demo/ (use demo username and password).