$(SolutionDir) is evaluated wrongly when reading project files

Project files that import props files from paths including $(SolutionDir) result in background build errors like these:

MyProjectFile.vcxproj: background build ERROR: The imported project "C:\MSVCProj\MyProjectFile\MySolution.props" was not found. Confirm that the expression in the Import declaration "C:\MSVCProj\MyProjectFile\MySolution.props" is correct, and that the file exists on disk.  C:\MSVCProj\MyProjectFile.vcxproj

The import declaration is as follows:

<ImportGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'" Label="PropertySheets">
  <Import Project="$(SolutionDir)MySolution.props" />
</ImportGroup>

The props file exists in the Solution directory, but Qt VS Tools is looking in the Project directory instead.

It seems that Qt VS Tools is using the project directory instead of the solution directory for this background build task.