Undefined index when update action, if change Acknowledgement operations from remote command to "Notify all involved"

Steps to reproduce:

1. Create action
2. Type action name
3. Open "Acknowledgement operations" tab
4. Add "remote command" operation
5. Save action
6. Edit action
7. Change "Remote command" operation to "Notify all involved"
8. Save
9. Press "details" in success message

Result:

Undefined index: opmessage [actionconf.php:222 ? CApiWrapper->__call() ? CFrontendApiWrapper->callMethod() ? CApiWrapper->callMethod() ? CFrontendApiWrapper->callClientMethod() ? CLocalApiClient->callMethod() ? CAction->update() in include/classes/api/services/CAction.php:850]