Consider a custom tag helper with this:

public class CustomTagHelper : TagHelper
{
  [HtmlAttributeName("foo")]
  public string? Foo { get; set; }

  // ...

And this razor markup:

... foo="bar" ... />

The foo attribute is missing in the rendered markup. If I remove the Foo property, it remains. So the tag helper removes such public properties.

I can’t find anything in the docs that describe this behaviour, so I don’t know whether it’s normal or the problem lies elsewhere.

Is this expected behaviour? If so, why does it work this way?

(My workaround is to re-add that attribute manually.)