Why doesn't it work to <Import /> this file, when it works when I replace the statement with just copy-pasting the three properties?

../../Setup.Version.proj

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
    <PropertyGroup>
        <InstallerMajorVersion>7</InstallerMajorVersion>
        <InstallerMinorVersion>7</InstallerMinorVersion>
        <InstallerBuildNumber>7</InstallerBuildNumber>
    </PropertyGroup>
</Project>

Works:

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="4.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
    <PropertyGroup>
        <InstallerMajorVersion>7</InstallerMajorVersion>
        <InstallerMinorVersion>7</InstallerMinorVersion>
        <InstallerBuildNumber>7</InstallerBuildNumber>
        <OutputName>asdf-$(InstallerMajorVersion).$(InstallerMinorVersion).$(InstallerBuildNumber)</OutputName>
        <OutputType>Package</OutputType>

Doesn't work:

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="4.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
    <Import Project="../../Setup.Version.proj" />
    <PropertyGroup>
        <OutputName>asdf-$(InstallerMajorVersion).$(InstallerMinorVersion).$(InstallerBuildNumber)</OutputName>
        <OutputType>Package</OutputType>

Here the variables just evaulate to empty strings... :( I'm certain the path to the imported project is correct.