Events seem to execute on a new thread - why?

First, I am not creating any new threads via invoke or any other intentional
means. As far as I know, there is just one thread, which is the main
thread.

My windows form class creates a new DeviceController() object which
initializes a serial port and defines a serial port event handler, which
processes the raw data from the serial port and then generates my custom
event (OnNewData).

public partial class LoggerForm : Form
{
DeviceController myDevice;

public LoggerForm()
{
InitializeComponent();
myDevice = new DeviceController();
myDevice.OnNewData += new
DeviceController.DeviceDataDelegate(DeviceDataEven tHandler);
}

void DeviceDataEventHandler(object sender, DeviceDataEventArgs e)
{
logTextBox.Text = e.DeviceData;
}
The consumer for my custom event is DeviceDataEventHandler(), which fires as
it should but produces the following run-time error: "Cross-thread operation
not valid: Control 'logTextBox' accessed from a thread other than the thread
it was created on."

How could this be? I thought an event was run on the same thread that
created it. It almost seems like the event is handled on a new thread.

Any ideas on why this is happening?
Thanks in advance.
Erik

Mark, that does help - I can probably solve it now.

But the basic question I'm grappling with is: why is my serial port
listener running on a separate thread in the first place? I never created a
new thread explicitly. The only thing I did as part of a method in
DeviceController is:

// create SerialPort, open COM port, add Serial Port event handler.
theSerialPort.DataReceived += new
SerialDataReceivedEventHandler(SerialDataParser);

SerialDataParser() just parses the serial port data and fires my
DeviceDataEventHandler() event. I don't understand see how this code is
running on a separate thread. I should mention this is with VS2005 and the
..NET framework 2.0.

Erik