Steps to Reproduce:
1. Copy text from another place. For my example I copied the first 4 paragraphs from here http://es.lipsum.com/feed/html
2. Create a new page and add an excerpt macro
Notice that the cursor is inside the body of the macro
3. Execute shortcut to paste
Result: The text is pasted outside/below the macro

Reproducible on Win 7, IE 11 with Confluence v5.5.3 and v5.8.9