In the Design Estimate Tool in Designer Express, the Buffer value is supposed to be typed as a percentage. For example, 5% is typed as 0.05. If this value is typed in the Buffer field and the field is exited (you tab or click out of the field), the value is removed and not used in the quantity calculation. However, if a value of 1.05 is typed, it is used in the quantity calculation and displayed in the Buffer field, as shown in the image below.
This also applies to cost items that have had a buffer value preset in the Cost Item Library Manager.
This behavior is caused by bug CLS-60646, "Buffer values not working for linear DFCs."
The work-around is to type the Buffer percentage values in the 1.nn format instead of 0.nn format. This bug is fixed in the latest patch for ArcFM 10.2.1b SP1.