Open Radar

 
Summary:
Occasionally, when selecting text, dragging it a short distance, and letting go, Safari gets stuck in some sort of "dragging" state. When this happens it is impossible to deselect the text or cancel this "mode". In addition, Safari windows do not perform any sort of drawing (i.e. websites will still update if they are something like a video or a gif, but the main Cocoa UI will not)–so things such as creating a new tab or new window perform these actions but there is no update. In the Command-Tab app switcher the cursor will show a small cursor with a prohibitory sign when on top of apps. I have tried things like selecting text in other apps and dragging, turning on mouse keys, and moving around windows in Mission Control, but these don't seem to resolve the issue; only quitting Safari does. Attached is a sysdiagnose taken right after restarting Safari when this issue occurred.

Steps to Reproduce:
1. Select some text, and start dragging it.
2. Try to deselect the text.

Expected Results:
The text is deselected.

Observed Results:
The text remains selected and Safari is stuck "dragging" the text, making it impossible to do anything else.

Version:
Release 36 (Safari 11.0, WebKit 13604.1.32.0.1)

Notes:
Regression from Safari 10.

Configuration:
MacBook Pro (Retina, 13-inch, Early 2015) running macOS High Sierra 10.13 Beta (17A315i)