Steps to reproduce:

1. Create a new glade file.
2. Add any widget with a label.
3. Enter some "World!" for the widget's label
4. Move the cursor to the beggining of the text you entered.
5. Try to type the world "Hello, "

Expected Result:

The label is now "Hello, World!"

Actual Result:

After each letter is typed, the cursor is moved to the end the label. So instead, the label is:
"HWorld!ello, "

This happens any time the text is changed (even when text is deleted), and makes editing labels in glade3 near-unusable.