I could reproduce the problem fairly easily:
I cannot reproduce this.
I followed your download & setup instructions exactly, navigated into a folder with 8 text files in, then:
Action: down-arrow to File2 & hit Insert
Result: File2 is selected, File3 has focus (as expected)
Action: right-click File2
Result: File3 loses focus & context menu opens (as expected)
Action: select "Edit" from the context menu
Result: only File2 remains selected & editor opens File2 only (as expected)