Cannot undo edit in Chrome Dev Tools

[NRDay]

Using Chrome dev tools to edit files, once Command S is pressed to save the change it is then not possible to Command Z and undo the change.

This works fine when editing the files whilst not using the BrowserSync proxy:-
http://localhost/tubby/

But not when viewing the sites using the BrowserSync proxy:-
http://localhost:3000/tubby/

Any one else had this issue?