Longname being ignored

I have an option for a start date.
` [Option('s', "startdate", Required = false, HelpText`

and am using the `-startdate 7/1/2020` as the arg

But no matter what I do, the args always end up being parsed as a shortname
`"nddate 7/1/2020"`

I would expect it to be `7/1/2020` and clean up that other stuff.

- Language: C#
- Framework: .Net Core 3.1
- OS: OSX 10.14
- IDE: Visual Studio Code

No source file, test, or entry point is named. First reproduce the issue using the supplied Option declaration and `-startdate 7/1/2020` argument, then trace the command-line parsing path that handles long names. Done means the value is parsed as `7/1/2020` rather than as a short-name argument, with a regression test covering the case.

Written by the indexing model from the issue text.