In Excel 2007 in data validation list, why does Excel perform a calculation when entering 2: 1 in the data validation list and how should I change this so no calculation is performed?

These are the selectable objects I have in my data validation list:

   -    ;2: 0,25;2: 0,5;2: 0,75;2: 1;3: 0,25;3: 0,5;3: 0,75;3: 1;4: 0,25;4: 0,5;4: 0,75;4: 1;5: 0,25;5: 0,5;5: 0,75;5: 1;6: 0,25;6: 0,5;6:0,75;6: 1;7: 0,25;7: 0,5;7: 0,75;7: 1

When I select for example "2: 0,25" then this is displayed exactly as in the data validation list. Only when there is a "1" after the colon, like "4: 1" or "3: 1" then Excel displays this as a decimal number (e.g. for "4: 1" is "0.17" displayed when I select "4: 1", and for "3: 1" is "0.13" displayed when I select "3: 1").

But I want that exactly the same is displayed as has been entered in my data validation list. What do I need to change so this works?