Yes it is odd. We have built over 20 duplexes in our community and have never had an issue until a few weeks ago. We hold the strapping back 3/4" on the 2nd floor fire wall, that way we can have continuous 5/8" drywall all the way up to the roof. The issue for us is between the floors, the rim joist/floor joists does not have the 5/8" continuous sheetrock. We have engineers, architects and our insulation company working on the issue. I will keep you posted.