Where did you define your input mask? If this is an input mask from the definition of the underlying table, your form should have picked it up when you created the form. Check the properties window for that field in Design View under the "Data" tab. See if it carried over to the Input Mask line for that field on the form. If not, you can fix this using VBA.
You should put this code in the BeforeUpdate event of that field:
Me.YourFieldName.InputMask = "00\-00\-0000;0;_ "
The last zero between the semi-colons at the end tells Access to store the literal (formatted) value in that field.
In future data entry, your fields will maintain their formatting exactly as you entered it.
For the existing records, put the same code in the form's OnOpen event, and that should clear it up. That will set the formatting up every time the form is opened.