From your question and comments, I'm guessing that the buttons and line-edit are in a QDialog, and that the selection/highlighting occurs due to the default/autoDefault property of buttons.
Normally, these properties will be set to False, but in a QDialog they are automatically set to True. The button that is the current default gets an additional frame drawn around it (even when it doesn't have the keyboard focus), and is activated whenever the return key is pressed.
You can of course prevent this behaviour by simply doing:
button.setDefault(False)
button.setAutoDefault(False)
for each button in the dialog.