Visual Studio - multiple property sheets with user macros

I recently split up my property sheets to reuse more of them:

From:

* Debug.props
* Release.props

Those files were copies of each other with only minimal changes like different user macros and debug/release flags.

I moved to:

* Common.props
* Debug.props
* Release.props

Now I define everything that's common for debug/release versions in the common file. In my debug/release files I define a user macro called:

Debug.props: $(KN_BUILD) = Debug
Release.props: $(KN_BUILD) = Relase

In my common file I use following:

outputDirectory: D:\AUSGABE\VW$(VW_VERSION)\$(KN_BUILD)\
postBuild: powershell.exe D:\Plug-Ins\Scripts\postbuild.ps1 $(VW_VERSION) $(KN_BUILD) $(TargetFileName)

Problem

Since I've split up my property files, the output file does NOT replace $(KN_BUILD) correctly anymore (it's replaced with blank), whereas the post build step still does. Why?

I'm using VS 2012, required by the SDK I use...