Bug Description
When using a text or number property, upon trying to change the initial value, the event that's fired only contains the old value.

Reproduction Steps

1. Create a properties window in any environment with a text input i.e.
   [
   {'type': 'text', 'name': 'Test', 'value': 'Testing...'},
   ]

2. Register a callback on that window to print every event.

3. Try to type another letter at the end of the text box that says 'Testing...'

4. Observe the 'PropertyUpdate' event that is printed. event['value'] is still 'Testing...'.

Expected behavior
The event['value'] should be 'Testing...<typed letter>'