Subtype markers are moved from .csproj to .csproj.user

[AdmiralSnyder]

Environment

VS 2026

.NET version

.net 10

Did this work in a previous version of Visual Studio and/or previous .NET release?

i don't think this is a regression

Issue description

existing
<Compile Update="WinTestForm.cs"> <SubType>Form</SubType> </Compile>
entries in the .csproj files are moved to the .csproj.user file arbitrarily (it happened to a coworker, and i just saw it in the changelog)
is this specified behaviour or a bug?

my goal would be to set these SubType-Markers in a Directory.Build.Props file for all *Form.cs files and all *UserControl.cs files in our codebase - will that work?

Steps to reproduce

I manually moved the values for a couple of forms into the .csproj because i moved the project in source control and the .csproj.user was stuck - and a day later, my change was reversed :-)

Diagnostics

[elachlan]

@Shyam-Gupta might be able to help?

[Shyam-Gupta]

@AdmiralSnyder .csproj.user file should not be checked into the source control. This is because this file is user specific. If you are using Git then you can add it to the .gitIgnore file so that it does not get pushed to the branch accidently.
The SubType metadata helps VS identify Form.cs or Form.vb files as WinForms files. There should be no requirement to add it the Directory.Build.Props file unless you are running into some issues.

cc: @merriemcgaw