MSBuild property being set to a value never defined (caching?) - visual-studio

Question

I have a .NET solution file that contains many projects, most of which are using the newer .NET SDK style .csproj format, but there is a project or two targeting .Net Framework 4.X and uses the older .csproj format.
I am extending the build process and have created 2 files in the solution root Directory.Build.props and Directory.Build.targets.
Problem: I have a particular property that is being set despite me belieiving that it shouldn't be set given the Conditions I have specified on my PropertyGroup.
To simplify the troubleshoot, I assigned a dummy starting value in my Directory.Build.props and then assigned a totally separate value in my Directory.Build.targets to see if my target ever runs.
Directory.Build.props
<Project>
<PropertyGroup>
<IncludeSymbols>true</IncludeSymbols>
<SymbolPackageFormat>snupkg</SymbolPackageFormat>
<MyProperty>Not set</MyProperty> <!-- property in question -->
</PropertyGroup>
</Project>
Directory.Build.targets
<Project>
<PropertyGroup Condition="
'$(tf_build)' != 'true' AND
'$(IsInnerBuild)' != 'true' AND
'$(Configuration)' == 'Debug' AND
'$(UsingMicrosoftNETSdk)' == 'true' AND
'$(BypassPublishLocalNugetPackages)' != 'true'">
<MyProperty>Set</MyProperty> <!-- property in question -->
<GeneratePackageOnBuild>true</GeneratePackageOnBuild>
<!-- Redacted addl misc. properties ... -->
</PropertyGroup>
<Target Name="BeforeBuild">
<Message Importance="high" Text="----------- BEFORE BUILD ------------"></Message>
<Message Importance="high" Text="MyProperty: $(MyProperty)"></Message>
<Message Importance="high" Text="GeneratePackageOnBuild = $(GeneratePackageOnBuild), UsingMicrosoftNETSdk = $(UsingMicrosoftNETSdk)"></Message>
<Message Importance="high" Text="----------- BEFORE BUILD ------------"></Message>
</Target>
<Target Name="AfterBuild">
<Message Importance="high" Text="----------- AFTER BUILD ------------"></Message>
<Message Importance="high" Text="MyProperty: $(MyProperty)"></Message>
<Message Importance="high" Text="GeneratePackageOnBuild = $(GeneratePackageOnBuild), UsingMicrosoftNETSdk = $(UsingMicrosoftNETSdk)"></Message>
<Message Importance="high" Text="----------- AFTER BUILD ------------"></Message>
</Target>
</Project>
To my surprise, the results of the compilation from within Visual Studio are inconsistent. I can compile a handful of times and the value of <MyProperty> will show Not set, however, after additional compilations and doing something as simple as modifying the .targets file by adding a space or new line and recompiling, the results change.
Initial compilation results
Rebuild started...
1>------ Rebuild All started: Project: MyProject, Configuration: Debug Any CPU ------
1> ----------- BEFORE BUILD ------------
1> MyProperty: Not set
1> GeneratePackageOnBuild = false, UsingMicrosoftNETSdk = "
1> ----------- BEFORE BUILD ------------
1> MyProject -> C:\MyProject\MyProject.dll
1> ----------- AFTER BUILD ------------
1> MyProperty: Not set
1> GeneratePackageOnBuild = false, UsingMicrosoftNETSdk = "
1> ----------- AFTER BUILD ------------
Random subsequent results
Note: Once this result below have been attained, the results do not seem to change at that point during additional compilations.
Also Note: The value displayed for <MyProperty> below is NOT the value set in my .targets file. That said, the condition in the .targets file is also not met anyway, so I'm not sure that matters.
Rebuild started...
1>------ Rebuild All started: Project: MyProject, Configuration: Debug Any CPU ------
1> ----------- BEFORE BUILD ------------
1> MyProperty: true
1> GeneratePackageOnBuild = false, UsingMicrosoftNETSdk = "
1> ----------- BEFORE BUILD ------------
1> MyProject -> C:\MyProject\MyProject.dll
1> ----------- AFTER BUILD ------------
1> MyProperty: true
1> GeneratePackageOnBuild = false, UsingMicrosoftNETSdk = "
1> ----------- AFTER BUILD ------------
I've done a fair amount of playing with these files to troubleshoot. Is it possible that the value is cached somewhere? Perhaps using a value that I had set at some point in the past?
I used SysInternals' ProcMon to look to see what files are being accessed to as a clue, but nothing stood out. Restarting Visual Studio does not help.
Any ideas why I'd have some ghost value appearing in my property?