http://bonsai.mozilla.org/cvsblame.cgi?file=mozilla/editor/libeditor/html/nsHTMLDataTransfer.cpp&rev=1.108&root=/cvsroot#752
selection->Collapse(selNode, 0);
selection->Extend(selNode, selOffset);
works for editor, but not for textarea's inputs and so.
Cut and paste should not select the pasted text hereafter.