Not sure what you mean Paul, as nothing much has changed you can fully view live data still!
Only if you don’t want to - you can switch it off with the bolt icon
So logging in and viewing works fine and even more easier if you switch to full preview mode by toggling the eye icon in the design view toolbar
It is no longer working for me unfortunately, so I used to have my page open, lets say the mail-list page, click the preview button, click the logout button on my page and it would redirect me just like a browser to my login page where i would put in my username and password and click LOGIN, this would then redirect to the Dashboard page lets say, I would turn off preview, and click refresh in design view, now i would be fully logged in and viewing all secure live data from my db.
What happens now though is I click the preview button, then click the logout button, it redirects me to my login page but like this.
So it is the code from the login page and not the physical rendered page?
Hmmm I think this is a different issue than the live data toggle.
One of the last design views improvements was to prohibit redirects but in your case you need those 
So maybe @patrick can just reenable those
I would be oh so happy, tell Patrick I would kiss his … for that feature back.
Back to your obsession with the backend stuff i see Paul 
As long as you go to the back of the queue
Confirmed 1.5.3 version has this all working beautifully again, thanks @patrick
