It is hard to describe the behaviour, so I made a GIF.
The macro was between Line A and Line B. After editing, it jumps to below Line B.
If you would like to try it out, you can install the macro from ZenUML Diagrams for Confluence(FREEMIUM) | Atlassian Marketplace.
This behaviour is also seen on DrawIO and Gliffy. We have not tested many other macros.