When grabbing a draggable element inside an iframe, the drag silhouette flies in from somewhere in the lower right instead of just appearing at the cursor position. I've observed this in Safari 11.0.1 as well as tech preview 43 on macOS 10.13.1. Example on JS Bin: http://jsbin.com/metezoyoge/1/edit?html,output
Thank you for the report! Do you know if this was working in earlier versions?
No I don't, sorry.
I suspect this is related to <rdar://problem/34936402>.
*** This bug has been marked as a duplicate of bug 181896 ***