Debugging environment in project properties is not saved or applied correctly in Visual Studio 2013

Steps to reproduce:

1. Open a Qt project in Visual Studio 2013.
2. Open project properties dialog
3. Select "Configuration Properties" - "Debugging" (in any configuration/platform)
4. Add ";C:\Temp" without quotes to the Environment setting. After this step my Environment is: PATH="$(QTDIR)\bin%3b$(PATH);C:\Temp
5. Save and close the solution
6. Open the same solution again
7. Open the project settings dialog
8. Select "Configuration Properties" - "Debugging" (in the same configuration/platform as step 4)

C:\Temp is now gone from the Environment setting. I have to manually update the Environment setting every time I open a Qt solution that expects to find resources/dependencies in PATH.

Note that the setting is stored in the vcxproj.user file in the same directory as the vcxproj file and if you open it in a text editor it looks like the path is saved correctly even though it won't be visible in the project properties or applied to a debugging session.

The formatting of the default also looks wrong. For example in my case: PATH="$(QTDIR)\bin%3b$(PATH), why is there no second " character and why the %3b escaped character instead of a normal semi-colon?