Following commit and merge of that PR, an inconveniant behaviour of the ‘Apply button’ appeared by introducing
self.applyButton.checkBoxControlsButtonToggleState = True
It seems to be a desired button behavior.
The check status of the checkbox controls the state of the toggle button. The problem is that whenever the button is clicked, the checkbox always gets unchecked. The button is no longer a toogle button (as it was before), but a simple button.
Now we can all live with that. Just in case you might deem it useful to restore back the previous parameter of the ‘Apply button’.
Thanks to the commit and its optmization.