[Safari 8] Pasting a copied or cut linewise selection adds an extra line

Repro (Safari only):

On codemirror.net, cut the line beginning with var editor: move the cursor to the beginning of the line, hold down Shift, press Down, release Shift, cut with Cmd + X, then paste with Cmd + V.

One more line is pasted than was cut, so after the operation you’ve got a blank line that wasn’t there before:

<script>
  var editor = CodeMirror.fromTextArea(myTextarea, {

    mode: "text/html"
  });
</script>

Only appears to repro for the new version of Safari that shipped with Yosemite (i.e. Safari 8). Perhaps a regression of this WebKit bug? https://bugs.webkit.org/show_bug.cgi?id=49288

[mallman]

Just FYI, still broken as of Safari 10.0.3.

[xzel23]

JavaFX WebView component is also affected (Version 11 and 12-ea). It’s also based on Webkit.