Yes, removing the -n is the way to fix your problem.  We went to quite 
a bit of effort to run user code from scratch on each Run/F5 using the 
subprocess.  Running without the subprocess is considered 'expert' mode 
these days. (Although it's still used on Windows if the user edits a 
file via the right click menu - something we hope to fix.)

There is a way around your difficulty - it involves using 'reload', but 
I didn't want to tell you about that too soon :-)

Now I need to look at Debian/Ubuntu to find out why the switch was 
added.  I run Debian, but not Ubuntu, and I use the command line 
pretty 
exclusively, so it didn't bite me.  If this is the way the IDLE package 
is configured, I'm surprised the issue hasn't been reported 
previously.  Thanks for the report!