The reason why the update is not made via "all properties", is because this is not the same thing:
- when add an onclick event via the Events tab, you actually create an <xp:eventHandler> child property for the button, which has an <xp:this.action> tag that contains your code.
- when you edit the onClick event of the button in All Properties, you add an <xp:this.onlick> property to the button
have a look at the source code of the XPage to see what I mean.
You can edit the code of the event handler via All Properties, but you need to navigate to the "Event Handler" under the button in the Outline view, and NOT to the button itself. Then, you will see that the "action" property has the right, up-to-date value.