Persistent syntax errors in non PS files

[jhoneill]

System Details

### VSCode version: 1.43.1 fe22a9645b44368865c0ba92e2fb881ff1afce94 x64

### VSCode extensions:
andyyaldoo.vscode-json@1.5.0
ms-azure-devops.azure-pipelines@1.165.1
ms-azuretools.vscode-azurefunctions@0.21.0
ms-dotnettools.csharp@1.21.15
ms-mssql.mssql@1.9.0
ms-vscode-remote.remote-containers@0.106.0
ms-vscode-remote.remote-ssh@0.50.0
ms-vscode-remote.remote-ssh-edit@0.50.0
ms-vscode-remote.remote-wsl@0.42.4
ms-vscode-remote.vscode-remote-extensionpack@0.20.0
ms-vscode.azure-account@0.8.8
ms-vscode.powershell@2020.3.0
ms-vscode.powershell-preview@2020.3.0


### PSES version: 2.1.0.0

### PowerShell version:

Name                           Value
----                           -----
PSVersion                      7.0.0
PSEdition                      Core
GitCommitId                    7.0.0
OS                             Microsoft Windows 10.0.18362
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Issue Description

When the default file type is PowerShell, and something else (e.g. JSON) is pasted into a new Window many syntax errors are detected and shown in the problem window

However if the document type changed to JSON or Plain Text the errors are not removed

Even if the file is closed the errors remain

Expected Behaviour

PowerShell syntax errors should only appear while the file is present and believed to be a PowerShell file.

[TylerLeonhardt]

If you made a single file edit, do the Problems go away? Like, add a single space in the file.

[jhoneill]

no, sadly

[TylerLeonhardt]

If you add another syntax error (like a random extra } or something) do you get additional Problems showing up?

[jhoneill]

No, once the type is changed to plain text, the errors are frozen. No new ones get added , but the old ones remain.

[TylerLeonhardt]

It seems like other extensions have this issue as well... I just reproed with the C# extension:

Plain text file, C# warning:

@jhoneill since I'm also seeing this with C# it's going to be an issue on VS Code itself:
https://github.com/Microsoft/vscode

Can you open an issue there?