It looks like this code in update.cpp does not respect the atomic option:

// *****************
if ( cc.get() == 0 )

{ shared_ptr< Cursor > cPtr = c; cc.reset( new ClientCursor( QueryOption_NoCursorTimeout , cPtr , ns ) ); }

if ( ! cc->yieldSometimes( ClientCursor::WillNeed ) )

{ cc.release(); break; }

if ( !c->ok() )

{ break; }

// *****************

And I'm seeing update_yield1 fail on my machine. (This test only runs weekly in bb.)