I’ve encountered a problem with the beta. If you have two panes open, the git panel open, and a git diff tab open in one of the panels, some actions (I tested Ctrl+S, Alt-Tab) will cause the git diff to be copied to the other window.
[Alt-Tab out, Alt-Tab in]
Does it happen in safe mode? Yes
OS? Ubuntu 17.04
Atom Version? 1.20-beta3 x64
Are there any errors in the console? No