Error from CMD+S whilst cursor is in post slug field

[cobbspur]

Issue Summary

When editing a post slug in PSM, saving with CMD+S whist the cursor is still in the slug field throws an error: Attempted to handle event 'becameError' on <post:id> while in state root.loaded.saved

Steps to Reproduce

1. Open PSM
2. Change slug leaving cursor in the slug field
3. Press Cmd+S

Two save requests will be triggered, the first will be successful and have the old slug, the second will have the new slug but will fail with an internal server error with the message Saving failed! Someone else is editing this post.

There are a two issues here:

• we should only fire a single save with the new slug
• the alert message should show the message received from the server not an internal Ember error

Technical details:

• Ghost Version: 1.0.0-alpha.21
• Browser/OS: Chrome

[aileen]

This happens also on LTS (see #8563).