I don't like the idea of [x] flashing quit instead of closing.  This patch, on top of the one for #24455, may not be perfect, but the two are definite improvements.  Unless I see something critically bad first, I want them in the upcoming releases.  Mark claims that his second patch for #15347 improves behavior for no subprocess.  But that was without this patch.

There is one situation not mentioned that I know is still glitchy.  Debug a program with input(prompt).  Run up to and including that line.  While the program is waiting for input, close with [x].  The shell prints '[DEBUG OFF]' after the prompt and '>>> ' on the next line.  But that is a fake prompt in that a statement entered will not be executed, but will be seen as the response to the pending input().

While there is a pending input (or any other blocked statement), the [Quit] button is disabled.  The close method should detect this 'program executing' condition and ask whether to kill it, just as if one tries to close IDLE under the same condition.

I am leaving this open, at least for now, at least for this.