When the save action is cancelled through an event listener, the error notification in the UI does not contain the thrown error message

Reproduction steps:

• Import the attached XAR which contains a listener on FileChangeDocumentSavingEvent cancelling them systematically with the reason "This event is cancelled by a custom listener."
• Perform editions in a page
• Save them as a new CR

Expected result:

• The CR cannot be saved and the notification in the editor displays the reason why

Obtained result:

• the CR cannot be saved but the notification only displays "Server error" as reason