Following code did work just fine in SS 2.3.4:

class XYZ extends Page {
...
function publish($fromStage, $toStage, $createNewVersion = false) {
// do something
return $this->extension_instances['Versioned']->publish($fromStage, $toStage, $createNewVersion);
}
...
}

since 2.4.0 i get an error, when publishing the site:
"Save and Publish" -> "Error saving content"

However the site is getting published and my custom code is getting executed...

* Did the function header of "function publish()" change?
* Do I still need to call $this->extension_instances['Versioned']->publish... ?
* Is it a bug in 2.4.0 b1?

Thanks for the Input.

sorry. forgot about the posting.

However, using onBeforeWrite solves the issue and seems to be the propper way.