In my spreadsheet I have a date column (col A) which I have in format
(dd/mmm/yy). I need to show the corresponding month in Col B, in MMM format
- April, May, etc.

I'd like the month to appear automatically in the corresponding cell in col
B when I type the date into col A, so that it looks like this:

A B
1 Month Date Added
2 Mar 10 March 2010
3 Apr 04 April 2010
4 May 05 May 2010

I managed to do this in A2 by using the formula =B2 and then changing the
format in cell A2 to MMM. However, I can't successfully copy this formula
down Col A to the other cells! The format is OK. When I try, it simply
copies down the month name, e.g. Mar, to all other cells regardless of which
month is in A3, A4, etc, viz:

A B
1 Month Date Added
2 Mar 10 March 2010
3 Mar 04 April 2010
4 Mar 05 May 2010

What am I doing wrong? Is there a better way to do this?