I have just tested out this issue and have been able to replicate what has been occurring. I entered Jira report UE-11269 into our bug database so that the issue may be resolved in a future release. I have also just seen that the Report has been fixed for the 4.8 version of UE4. I am unsure as to when this version of UE4 will be released but I will be sure to let you know as soon as I hear anything.
Is there no chance at all for another 4.7 HotFix with this fix included? I did hear that mobiles are going to get some love with the 4.8 but a squashed viewport is quite a bug to be honest, it makes portrait oriented games simply unpublishable. And it will probably take 2-3 months at least for the 4.8 to get released.