try something

Author: drewcassidy

KSPCommon.props

@@ -104,6 +104,11 @@
     <KSPBT_GameRootSource>steam</KSPBT_GameRootSource>
   </PropertyGroup>
 
+  <!-- Calculate KSPBT_ManagedPath -->
+  <PropertyGroup Condition=" '$(KSPBT_ManagedPath)' == ''">
+    <KSPBT_ManagedPath>$(KSPBT_GameRoot)/$(_KSPBT_ManagedRelativePath)</KSPBT_ManagedPath>
+  </PropertyGroup>
+
   <!-- set the start action so that you can launch directly from VS -->
   <PropertyGroup>
     <StartAction>Program</StartAction>

KSPCommon.targets

@@ -2,11 +2,6 @@
 <Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <Import Condition=" '$(KSPCommonPropsImported)' == '' And Exists('$(MSBuildThisFileDirectory)KSPCommon.props') " Project="$(MSBuildThisFileDirectory)KSPCommon.props"/>
 
-  <!-- Calculate KSPBT_ManagedPath -->
-  <PropertyGroup Condition=" '$(KSPBT_ManagedPath)' == ''">
-    <KSPBT_ManagedPath>$(KSPBT_GameRoot)/$(_KSPBT_ManagedRelativePath)</KSPBT_ManagedPath>
-  </PropertyGroup>
-
   <!-- Import references -->
   <ItemGroup Condition=" '$(KSPBT_ReferenceSystemAssemblies)' == 'true' ">
     <Reference Include="$(KSPBT_ManagedPath)/System.dll">