Copy and Paste does not work as advertised

I am trying to replace a segment of the sound with the adjacent sound to remove a sniff.

Everything I have tried does not allow me to paste over/overlap the selected area. It just pastes it into an adjacent area. Am I missing something, or is this a bug?

Pasting behaviour set to overlap

Area copied

Just utilising the paste option

Just utilising the paste and overlay option

As a result, it pastes it adjacent to the area I want pasted over.