I decide to conduct tests on delete everything and these are my findings/objects that won't be deleted by delete everything. EDIT: Delete everything also deletes locked objects Gameplay/Weapons: Assault Rifle Battle Rifle Battle Rifle Halo 2 Boltshot Lightrifle SAW Storm Rifle SuppressorGameplay/Powerups: Active camouflage Damage Boost Overshield Speed BoostGameplay/Vehicles: Mongoose Gungoose Warthog Scout Warthog Machine Gun Warthog Gauss Warthog Rocket Ghost Scorpion Mantis PhaetonGameplay/Turrets Shade Turret Shade Turret Anti-Air Gauss Turret Full Plasma Turret Full Splinter Turret FullProps/Explosives Barrel UNSC Fuel Canister UNSC Fusion Coil UNSC Fusion Coil Forerunner Core Fusion Coil CovenantProps/Toys Kill Ball Most of these will probably be fixed by the next uplate but the more you know. The map is in my Bookmarks titled "Test Delete" GT=REX JOURNEY EDIT 2: Did some more testing with weapons/powerups/vehicles/turrets which amounted to 57 objects however when I deleted everything the first time I still had 57 objects. Deleting everything a second time reduced the pieces to 33 (not everything respawns as it should, some objects do not respawn when the delete everything happens). What bothers me even more is that reloading the map reduced the piece count to 28. Also if you have anything listed above when you delete all and those 'bugged' objects are on top of objects not bugged the 'bugged' items are launched from their initial respawn, making it harder to find and delete them.
A tip to ensure all things got deleted until this fix occurs - place 256 sized floors under your map, delete all and if anything is set to normal it will land on the floor and delete any remaining floating objects. I never really understood the want to delete all though... Why not just start on a new canvas and delete the old file? Delete all of a same object makes sense and delete all unlocked objects.