refresh page F5 don't close port 4010

Steps:

1. open file: Helloworld.exe
2. open browser FF
3. enter URL: http://127.0.0.1:4010
4. refresh page: click key F5 (2-4 click)

Expected Results:
msg in browser: 'Hello, World'

actual result:
msg in browser: 'Hello, World', but server don't close port 4010