Cell format - custom date

[Ducatisto]

I may be looking way too far from the end of my nose but this one has me stumped. I have two workbooks which track every day of the year, each column headed by a date. My first workbook is good but my second is playing me up! As it happens the cells are formatted Custom - d/m and the date this particular sheet starts with is 04/10/2009. Now, inputting any variation of that date; 4/10, 4/10/9, 4/10/09, 04/10 and all the rest, it ALWAYS enters 10/4/09! Ok, I tried by entering a date further into the month, say 21/10 and it displays correctly so you can see why I am puzzled. I just entered 10/10 and yes, obviously it entered correctly but as soon as I entered 09/10 it entered 10/09/2009. Can anyone replicate this? I have tried all dates throughout the year and the only issues I have are from 01/10 to 09/10.

This particular issue has not been solved per se but I got over it by copying and pasting the page into a new workbook whereupon the data formatting in the cells worked, extremely bizarre. It was due to this that I could not upload a sample to show you as it would not replicate the issue.