Created attachment 411566 [details]
Screen recording demonstrating bug, and variation with menu item selected

Steps to repeat this bug:

Step 1. In System Preferences > Keyboard > Shortcuts > App Shortcuts, reassign the keyboard shortcuts of Safari for 'New Private Window' to Command-n and 'New Window' to Command-Shift-n

Step 2. Restart Safari.

Step 3. In the File menu, note that the keyboard shortcuts have been remapped, and the new shortcuts are displayed in the menu next to 'New Private Window' and 'New Window'

Step 4. Press Command-n 


Expected Result: a new 'private' window is opened

Actual Result: a new 'standard' window is opened

Comments: The remapping of menu item shortcuts appears to work with most of Safari's menu items, unless the chosen shortcut is Command-n. Interestingly, if Safari's File menu is currently active (selected with mouse), the behaviour of Command-n changes to the expected action, and in this case opens a New Private Window as expected.