Take a look in the scriptmath3d.cpp function RegisterScriptMath3D_Native().
void RegisterScriptMath3D_Native(asIScriptEngine *engine)
{
int r;
// Register the type
r = engine->RegisterObjectType("vector3", sizeof(Vector3), asOBJ_VALUE | asOBJ_POD | asOBJ_APP_CLASS_CAK); assert( r >= 0 );
I believe addding the asOBJ_APP_CLASS_ALLFLOATS flag will make the tests pass successfully.