There were two problems addressed here.
First, the call to Diagram was causing the second error to be added to the ParseResult.Errors collection. The diagram call, was being invoked by the debugger as part of the ParseResult.ToString() method. Causing the number of errors to change when inspecting a parse result.
The second issue was the error message text. It was implying that the option expected a single value, when its arity allowed for more.
There were two problems addressed here. First, the call to Diagram was causing the second error to be added to the ParseResult.Errors collection. The diagram call, was being invoked by the debugger as part of the ParseResult.ToString() method. Causing the number of errors to change when inspecting a parse result.
The second issue was the error message text. It was implying that the option expected a single value, when its arity allowed for more.