Enforcement of defensive holding- NFL

[Adambr2]

This one is driving me nuts because no matter how much I look this one up I have yet to find an explanation, even in the NFL rule book.

Routinely, I'll see a 5 yard defensive holding added to the end of a positive play rather than simply declined like any defensive offside or other minor defensive penalty would be.

Yet, this doesn't happen every time. At the end of a long play by the Steelers tonight, a 5 yard defensive holding was declined rather than added to the end of the run.

I can find nothing anywhere stating that a defensive holding penalty is unique in any way in this fashion.