I noticed a bug within Excel when using the Ctrl+Copy command:

When you use the Copy and Paste commands by holding Ctrl to copy multiple
cells (non-adjacent) from a Microsoft Excel document to another Microsoft
Excel document (separate instance), the pasted range will include the cells
between the non-adjacent regions.

For Example: If you use the Ctrl + Copy command to copy cells A1 and A10,
the pasted data will include entire range of A1:A10.

Note: The problem only occurs when copying and pasting data across multiple
instances of Excel that are open. This does not happen when pasting to the
same document or another document which was opened within the first instance
of Excel.

This problem occurs on Microsoft Office 2003, 2007 and also 2008 for Mac.