Linked Cells to missing workbooks shows either 1 or 0

1. Open a new Excel file (XXX.xlsx). Put a link in A1 to an external spreadsheet that you don’t have. The linked value is zero.
2. Close XXX.xlsx and then create a new Excel file (YYY.xlsx). Create an identical link to the same external spreadsheet (that you don't have). This has a different value (one) for the linked cell when it was saved.
3. At this point you should be convinced that the value of cell A1 is zero in spreadsheet XXX and is one in spreadsheet YYY.
4. Now, with YYY still open, reopen XXX. Cell A1 is zero as expected.
5. Now switch your view to spreadsheet YYY. You will see that the value has changed from one to zero even though you have made no changes to that spreadsheet.
6. In fact you can switch the values for either spreadsheet simply by closing and reopening the other one.

Is this a bug or "feature"?