If you create a new C# Program query and run this code snippet...

void Main()
{
for (int i = 0; i < 10000; i++)
{
Console.WriteLine(String.Format("{0:D6} Did all the lines break?", i));
}
}

You will see:

There is a line break missing at position 4055.
There is an extra line break inserted at position 5407.

There is a line break missing at position 6759.
There is an extra line break inserted at position 8111.

There is a line break missing at position 9464.

This is consistent across LinqPad 4 and 5, Windows 10 and Windows Server 2008, LinqPad free and Premium.

Tested with a clean install on a new machine, still happens.