This behavior is new to the latest update - in past versions of Photoshop when you duplicated a layer that was in a stack of layers which used the same clipping mask, the new duplicate layer would retain the original layer's clipping mask (note that this is only when right-clicking and selecting "duplicate layer", or in my case using a shortcut key to duplicate a layer). However, now when you duplicate a layer in a stack of layers with the same clipping mask, the new duplicate no longer has the original layer's clipping mask, and all layers above which previously used the original clipping mask, now will use the new duplicate layer as the clipping mask.
WHAT GIVES??? This is hugely annoying - does anyone have a fix to this or a workaround? i scoured the preferences for an option to fix this but found nothing.