This is a quick fix for Bug:373338 which allows multiple layers to be cloned simultaneously. Perhaps the layers could be sorted so that it goes above the highest selected layer instead of the
active layer, but it's hard to say what the default behavior should really be.
Alternatively, if add operations should only work on one layer at a time, I could add a
Quick Clone option as a work around for this bug. This seems like the desired behavior for trying to add a clone layer when multiple layers are selected.