Two errant clicks close to each other... created a lot of clean up work. Ask me how I know 
(It ended up taking less time to just start over, deleting and recreating the whole Channel Collection.)
And when it happened a second time..........
I've been burn my this so may times. I never seem to learn 
How do you know? 
Voted. 
Seems fair. We’ll look into it.
This has been resolved in the latest Pre-release:
2 Likes
Thank you!
I noticed two minor issues with the message:
- The channel count shown is currently the total channel count (new channels about to be added + existing channels already in the collection) rather than just the new channels about to be added
- It's missing the word "to":
Are you sure you want to add 123 channels [to] the News Channel Collection?
Yikes, that was sloppy. OK, it's fixed up in the latest pre-release: