Create a minigame, set skis and rockets (or any radius damage weapon) as the weapons, get on the skis and hit yourself with a rocket. You will automatically dismount off your skis and receive console errors. I recreated this bug with no add-ons running at all, on a default map.
*** Phase 1: Download Datablocks & Targets
*** Phase 2: Download Ghost Objects
*** Phase 3: Mission Lighting
Successfully loaded mission lighting file: 'Add-Ons/Map_Bedroom/bedroom_1758a064.ml'
Mission lighting done
Heedicalking spawned.
base/server/scripts/allGameScripts.cs (22856): Register object failed for object (null) of class Projectile.
base/server/scripts/allGameScripts.cs (22857): Unable to find object: '0' attempting to call function 'setScale'
BackTrace: ->ProjectileData::onExplode->ProjectileData::radiusDamage->ShapeBase::Damage->WheeledVehicleData::Damage
Set::add: Object "0" doesn't exist
base/server/scripts/allGameScripts.cs (22884): Unable to find object: '' attempting to call function 'spawnVehicle'
BackTrace: ->ProjectileData::onExplode->ProjectileData::radiusDamage->ShapeBase::Damage->WheeledVehicleData::Damage
Issuing Disconnect packet.
Exporting server prefs
Exporting client prefs
Exporting client config
Exporting rtb prefs
Shutting down the OpenGL display device...
Making the GL rendering context not current...
Deleting the GL rendering context...
Releasing the device context...
