Dear Aren,
I have a similar issue: I want to upgrade a project, where I use a lot of checkboxes with attached UIButtonTween triggered by OnActivate.
Example NGUI 2.7x:
When activating the checkbox, the object linked to the UIButtonTween is enabled and the attached tween is played.
When deactivating the checkbox, the object plays the tween reverse and is disabled.
NGUI 3.x:
I replaced UICheckbox by UIToggle and UIButtonTween by UIPlayTween (triggered by OnActivate).
Activating or deactivating the UIToggle does not seem to trigger the UIPlayTween component.
When sending OnActivate(bool) to the UIPlayTween object it works as expected.
I checked the "Example 2 - Interaction" scene. UIPlayTween works well with OnClick events. (p.s. you should update the text there).
Any idea what I can do?