Percentage values should be specified using a single or double data format: ie. 5.00% is actually stored as 0.0500, and 78.33% is actually stored as 0.7833. This is done this way to lend functionality to calculated fields.
For example, if you want to calculate a given employees percentage of total sales you would divide his sales figure by the total sales figure. This returns a decimal value like "0.2648". Using the percentage format on this calculated field will display this information as "26.48%".
If you decide you must use integer data types with the percentage format, try modifying the "Control Source" property of the control:
=[MyField]/100