Binding text box to object's property not properly bound!

[teddysnips]

WINDOWS FORMS

I have a form with a BindingSource connected to an Object.

The controls on the form are bound to the properties of the Object.

I have a text box txtOtherVoltage where the Text property is bound to
the VehicleVoltageUsage property of my object.

When I load the form, the txtOtherVoltage text box shows the correct
data from the object.

However, I want to be able to change the value of the text box
programmatically and have it saved into my object (which is later
serialized in XML)

If I run this code:

this.txtOtherVoltage.Text = "12";

the value of the corresponding property in the object is NOT updated.

However, if I do this:

m_data.VehicleVoltageUsage = 12;

(with m_data being my current instance of the object) all is well.

Which rather negates the point of data binding, non? So what am I
doing wrong? I have a sneaking suspicion that it's something to do
with the property being of type int, and the text box having a string
written to it. However, I am very new to C# and I might be totally
off the mark. Other controls on the form (including a DataGrid,
CheckBox etc.) all work fine.

TIA

Edward