A bit hard to explain.
Forgot to add a backslash after the colon while trying to create a directory. Received no error but couldn’t find the created folder.

using System.IO;

private static void CreateWrongDirectory()
{
    var falseCPath = @"C:TempMyTest";
    var falseDPath = @"D:TempMyTest";

    var currentDirectoryD = @"D:TempCurrentDirectory";
    Directory.CreateDirectory(currentDirectoryD);

    Directory.SetCurrentDirectory(currentDirectoryD);
    Console.WriteLine($"Working Directory: {Directory.GetCurrentDirectory()}");

    Console.WriteLine();
    Console.WriteLine($"Trying to create "{falseCPath}"");
    var di = Directory.CreateDirectory(falseCPath);
    Console.WriteLine($"Created "{di.FullName}"");
    di.Delete();

    Console.WriteLine($"Trying to create "{falseDPath}"");
    di = Directory.CreateDirectory(falseDPath);
    Console.WriteLine($"Created "{di.FullName}"");
    di.Delete();

    Console.WriteLine();

    var currentDirectoryC = @"C:TempCurrentDirectory";
    Directory.CreateDirectory(currentDirectoryC);

    Directory.SetCurrentDirectory(currentDirectoryC);
    Console.WriteLine($"Working Directory: {Directory.GetCurrentDirectory()}");

    Console.WriteLine();

    Console.WriteLine($"Trying to create "{falseCPath}"");
    di = Directory.CreateDirectory(falseCPath);
    Console.WriteLine($"Created "{di.FullName}"");
    di.Delete();

    Console.WriteLine($"Trying to create "{falseDPath}"");
    di = Directory.CreateDirectory(falseDPath);
    Console.WriteLine($"Created "{di.FullName}"");
    di.Delete();
}

Output is:

Working Directory: D:TempCurrentDirectory

Trying to create "C:TempMyTest"
Created "C:TempMyTest"
Trying to create "D:TempMyTest"
Created "D:TempCurrentDirectoryTempMyTest"

Working Directory: C:TempCurrentDirectory

Trying to create "C:TempMyTest"
Created "C:TempCurrentDirectoryTempMyTest"
Trying to create "D:TempMyTest"
Created "D:TempMyTest"

How come that depending on the current directory and drive letter a “wrong” path once gets created and the other time not?