Issue with the Nu validator

I have noticed that the HTML Validation Service at https://validator.w3.org/ seems to ignore when you manually select a character encoding and upload a file to be validated.

For example if I go to "validate by file upload" and pick a file that does not have a "meta charset" tag in it, and select my character encoding from the pulldown menu, then I get "Error: The character encoding was not declared. Proceeding using windows-1252."  (Even with the "meta charset" tag this may happen, but only intermittently.)

This only happens with the "Nu" validator.  How can I use the legacy validator instead?

Thanks,
Jonathan