Cosmos: Broken background color

Symbol with a different color appears after each line break 😦

Code:

Console.Clear();
// Fill background
Console.BackgroundColor = ConsoleColor.Cyan;
for (int i = 0; i < (80 * 25); i++)
    Console.Write(" ");
Console.CursorTop = 0;
//
while (true)
{
    Console.WriteLine("test!");
    Thread.Sleep(1000);
}

But if do not set background color, it’s all right: