Is this a King County thing?
As far as I know King County is using the IRC code same as every other county in the state, and staples are allowed under the IRC, except in engineered shear panels where 8d nails are specified. A engineered shear panel can be specified with staples and is allowed in the IRC, but most engineers just specify 8d's.
Check IRC Table R602.3(2)
I looked at the King County DDES website, and I didn't see any exceptions or sections not adopted applying to this. The only chapters not adopted are 11, and 25 thru 40.
16.05.010 Adoption. The International Residential Code for One- and Two-Family Dwellings Code, as amended in chapter 51-52 WAC, effective July 1, 2007, as published by or jointly with the International Code Council, Inc., together with appendices, amendments, additions, deletions and exceptions hereinafter adopted by reference, together with the Washington state building code and with King County modifications which shall be adopted and codified in this chapter are adopted as the King County International Residential Code for One- and Two-Family Dwellings code and hereinafter referred to as the International Residential Code, "IRC." Chapter 11 and Chapters 25 through 40 are not adopted. The energy code is regulated by chapter 51-11 WAC; the plumbing code is regulated by chapter 51-56 WAC; the electrical code is regulated by chapter 296-46B WAC; and Appendix G is included in adoption of the International Residential Code. (Ord. 15802 § 74, 2007: Ord. 14914 § 269, 2004).