Dmytro says " This is known bug #91293, the fix should be available with the next platform and Edit UI updates." so you should log in to your site and go to add-ons and install the platform updates from there also you might ensure that you have the latest versions of EPi assemblies in your solution by updating the nuget packages in visual studio (assuming you are doing this in your own environment / test env before live env)

Let me help you find the patches as this is what you really want. It's so damn confusing the way the chose to do it, and its not easy to find the information regarding this.

I guess you have to keep yourself updated here (not easy to find really):
http://world.episerver.com/Download/Releases/

Here is the explanation on how to install the patches:
http://world.episerver.com/Documentation/Items/Installation-Instructions/Installing-EPiServer-Patches/

And here is the patch you would want to install:
http://nuget.episerver.com/en/OtherPages/Package/?packageId=EPiServer.CMS.Core

Then it is time to get it working with source control and the alloy mvc templates (cause you do actually need some libraries from the [Libraries] folder that is being copied from the post build event the article above just told you to remove. All i can say ... good luck :) 

Hmmm something funny is happening with the last link to the nuget package. It goes to the wrong version.

What you need is: EPiServer.CMS.Core 7.0.586.16

Thank you for your inputs.

After at least a days work, we finally managed to install patch 3 and upgrade to EPiServer 7.1.

It seems nothing has changed, upgrading anything EPiServer-related it just ... painful!

@Jakob Gade  

please help me find Patch 3 

I have installed CMS 7.1.10 using Add On's is it all ?

After 7.5 it's much smother upgrades at least. Getting better and better. I still remember upgrading from 4 to 5. Now that was pure pain :)