------EVERYONE WHO HAS USED ARCGIS ONLINE HAS DONE THIS------
While administering ArcGIS Online the Space between Remove Pop-up and Configure Pop-Up is less than a millimeter. Actually there is No space. TWICE today, I have hit Remove Pop-Up instead of Configure Pop-Up.

***POOF*** - GONE.
If it's a custom HTML pop-up wiht attachemnents, Links, & everything is just perfect, this can really sour your day.
Please warn us, or give us an "Oh Crap!" button
I know I can cut & past the code, into a text editor, and I do. But you know when you get into the groove, making little changes and stuff like that, it just gets away from you 1/2 hour goes by really quickly.
Then hitting the wrong button loses that work!