Heat.exe throws error for valid MSBuild 4.0 schema element "Label"

[wixbot]

The following error is given by heat (used as part of build event) to harvest files from another project (.csproj).

heat.exe(0,0): error HEAT5305: Failed to load project E:\Development\XXXX\XXXX\XXXX\XXXX.csproj:
The attribute "Label" in element is unrecognized.

The project being harvested has a valid MSBuild 4.0 element, but heat deems that it is not (perhaps validating using an old version schema?).

I'm using VS 2013 Update 2 and WiX Toolset 3.8

Refer the following link for related information on the issue:
Slow Cheetah Issue 133

Originally opened by jaans

[wixbot]

Originally changed by jaans
Release changed from v3.8 to

[wixbot]

Release set to v3.x