keikai invokes onClipboardPaste listener twice unexpectedly

Steps to Reproduce

    <spreadsheet id="ss" hflex="1" vflex="1"
                 showFormulabar="true" showContextMenu="true" showToolbar="true"
                 showSheetbar="true" showSheetTabContextMenu="true" maxVisibleRows="100" maxVisibleColumns="40"
                 onCellSelection="" onClipboardPaste="System.out.println(event)"/>

1. input a at A1
2. press ctrl+c to copy A1
3. press ctrl+v to paste at A2
check the server console

Current Result

server console prints 2 onClipboardPaste event

Expected Result

server console prints 1 onClipboardPaste event

Debug Information

1. if no onCellSelection listener is registered, this bug doesn't happen.
2. the bug only happens at the first pasting. If you paste again, keikai will invoke the onClipboardPaste listener once which is expected.

Workaround

remove onCellSelection listener