Highlighting a block of cells that contain one or more embedded Notes, and then 
drag/drop to move those cells causes deletion of all cell contents, except for 
the embedded notes.  

If any one or more of the highlighted cells contain a note, all cell contents 
are lost, including data and formulas.  Any custom Formatting of those moved 
cells is preserved.  

If you highlight those same cells and perform the Cut and then Paste 
operations, all contents are preserved, as expected.  Therefore, I conclude 
that it is the drag/drop mouse operation that sets up the error condition.