First, I am impressed by the Smart Mask 2.0, and this post is not about the result you get (good or bad), but how it treats stills. I had a 5 second still photo on the timeline, and let it process on the first frame (as all frames are the same anyway in a still). However, using the complete button, it analyzed and processed every frame in the 5 second clip which is insane (and not needed if it is a still), as it takes a very long time.
Obviously the smart mask cannot know it is a still (it is not that smart!), and as such, the behavior is to be expected.
I would suggest to add an extra button in the GUI to indicate it is a still and so all further frames do not need to be analyzed and only processed to copy the mask to all frames.
As a workaround to overcome this "time looser" I reduce the duration of the still to one frame, run the smart mask, complete it, and then increase the clip duration to the wanted duration, although it saves some time, this workaround is also not optimal.