Wpf textblock text binding not updating
The second Text Box uses the Lost Focus value, which is actually the default for a Text binding.
It means that the source value will be updated each time the destination control loses focus.
You can refer to the samples cited in this topic for more information.
In addition, you can look at Implement Property Change Notification.
Text property has a default Update Source Trigger value of Lost Focus.
As of writing, all properties except for the Text property, is updated as soon as the property changes (Property Changed), while the Text property is updated when focus on the destination element is lost (Lost Focus).
Default is, obviously, the default value of the Update Source Trigger.
For those situations where you need more control of the process, this property will definitely help though.
Just make sure that you don't update the source value more often than you actually need to.
In the previous article we saw how changes in a Text Box was not immediately sent back to the source.