Csc compiler error after upgrading to VS2015 Update 3 (order of import statements)

Description

After upgrading to VS2015 Update 3 I noticed that some WebAPI projects targeting framework v4.6.1 were coming up with the following error:

Build FAILED.

       "D:\Code\my-project\src\WebApiProject.Tests.Unit\WebApiProject.Tests.Unit.csproj" (Build target) (1) ->
       "D:\Code\my-project\src\WebApiProject\WebApiProject.csproj" (default target) (5) ->
       (CoreCompile target) ->
         C:\Program Files (x86)\MSBuild\14.0\bin\Microsoft.CSharp.Core.targets(76,11): error MSB4064: The "ChecksumAlgorithm" paramete
       r is not supported by the "Csc" task. Verify the parameter exists on the task, and it is a settable public instance property. [
       D:\Code\my-project\src\WebApiProject\WebApiProject.csproj]
         C:\Program Files (x86)\MSBuild\14.0\bin\Microsoft.CSharp.Core.targets(67,5): error MSB4063: The "Csc" task could not be initi
       alized with its input parameters.  [D:\Code\my-project\src\WebApiProject\WebApiProject.csproj]

Repro steps

Paket orders the import statements like so;

  <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
  <Choose>
    <When Condition="$(TargetFrameworkIdentifier) == '.NETFramework' And ($(TargetFrameworkVersion) == 'v4.6.1' Or $(TargetFrameworkVersion) == 'v4.6.2')">
      <PropertyGroup>
        <__paket__Microsoft_Net_Compilers_props>Microsoft.Net.Compilers</__paket__Microsoft_Net_Compilers_props>
      </PropertyGroup>
    </When>
  </Choose>
  <Import Project="..\packages\Microsoft.Net.Compilers\build\$(__paket__Microsoft_Net_Compilers_props).props" Condition="Exists('..\packages\Microsoft.Net.Compilers\build\$(__paket__Microsoft_Net_Compilers_props).props')" Label="Paket" />
  <Choose>
    <When Condition="$(TargetFrameworkIdentifier) == '.NETFramework' And ($(TargetFrameworkVersion) == 'v4.6.1' Or $(TargetFrameworkVersion) == 'v4.6.2')">
      <PropertyGroup>
        <__paket__Microsoft_CodeDom_Providers_DotNetCompilerPlatform_props>Microsoft.CodeDom.Providers.DotNetCompilerPlatform</__paket__Microsoft_CodeDom_Providers_DotNetCompilerPlatform_props>
      </PropertyGroup>
    </When>
  </Choose>
  <Import Project="..\packages\Microsoft.CodeDom.Providers.DotNetCompilerPlatform\build\$(__paket__Microsoft_CodeDom_Providers_DotNetCompilerPlatform_props).props" Condition="Exists('..\packages\Microsoft.CodeDom.Providers.DotNetCompilerPlatform\build\$(__paket__Microsoft_CodeDom_Providers_DotNetCompilerPlatform_props).props')" Label="Paket" />

Ordering them instead like this fixed the issue;

  <Choose>
    <When Condition="$(TargetFrameworkIdentifier) == '.NETFramework' And ($(TargetFrameworkVersion) == 'v4.6.1' Or $(TargetFrameworkVersion) == 'v4.6.2')">
      <PropertyGroup>
        <__paket__Microsoft_Net_Compilers_props>Microsoft.Net.Compilers</__paket__Microsoft_Net_Compilers_props>
      </PropertyGroup>
    </When>
  </Choose>
  <Import Project="..\packages\Microsoft.Net.Compilers\build\$(__paket__Microsoft_Net_Compilers_props).props" Condition="Exists('..\packages\Microsoft.Net.Compilers\build\$(__paket__Microsoft_Net_Compilers_props).props')" Label="Paket" />
  <Choose>
    <When Condition="$(TargetFrameworkIdentifier) == '.NETFramework' And ($(TargetFrameworkVersion) == 'v4.6.1' Or $(TargetFrameworkVersion) == 'v4.6.2')">
      <PropertyGroup>
        <__paket__Microsoft_CodeDom_Providers_DotNetCompilerPlatform_props>Microsoft.CodeDom.Providers.DotNetCompilerPlatform</__paket__Microsoft_CodeDom_Providers_DotNetCompilerPlatform_props>
      </PropertyGroup>
    </When>
  </Choose>
  <Import Project="..\packages\Microsoft.CodeDom.Providers.DotNetCompilerPlatform\build\$(__paket__Microsoft_CodeDom_Providers_DotNetCompilerPlatform_props).props" Condition="Exists('..\packages\Microsoft.CodeDom.Providers.DotNetCompilerPlatform\build\$(__paket__Microsoft_CodeDom_Providers_DotNetCompilerPlatform_props).props')" Label="Paket" />
  <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />

Expected behavior

Microsoft.CSharp.targets is below that of the Net.Compilers and CodeDom.Providers prop imports.

Actual behavior

Microsoft.CSharp.targets is above that of the Net.Compilers and CodeDom.Providers prop imports.

Known workarounds

Move them manually and correct after each Paket update.

Related information

Paket version 3.4.0.0

Start by tracing Paket's generated project-file import ordering, using the shown WebApiProject.csproj sequence and the Microsoft.CSharp.targets, Microsoft.Net.Compilers, and Microsoft.CodeDom.Providers.DotNetCompilerPlatform imports. Reproduce the build with VS2015 Update 3 and confirm that Microsoft.CSharp.targets is emitted below the package property imports and the MSB4064/MSB4063 errors no longer occur.