I see that, too, Bob. Not sure why it is like that but you’re right. Inferencing doesn’t seem to be active with Stamp. Have a look at this, though.
It looks like the intent is not to have the stamped terrain faces moved to meet the slab or whatever. The expectation is that you set the height of the stamping and move the slab or whatever down to meet it.
Still, it seems like inferencing would be useful here since there’s no way to set a height like you could with Push/Pull