RSS feed, why does one work and not the other??

[pityocamptes]

Using this in the CMS widget area. I need the HTTPS for the site, so I ran the original RSS through feedburner. Can someone tell me why this one works in CMS widget:

http://feeds.reuters.com/Reuters/worldNews

but this one does not:

https://feeds.feedburner.com/reuters/GYXq

when both are valid????