OS: x64 Windows 10 Professional 1903
Python: Python 3.8 package (3.8.5) installed from Microsoft Store

Steps to reproduce the bug:

1. Create empty file (right click anywhere, "New" -> "Text document", rename to "insert_filename_here.py"). File size is 0 bytes.

2. Open the file in IDLE

3. Type "import os" (actually content could be anything). IDLE title bar changes by prepending asterisk (*) to the filename, indicating file is modified but not saved yet.

4a. Press Ctrl+S  --> nothing happens
4b. Click "File" -> "Save"  --> nothing happens
4c. Click "File" -> "Close".  Dialog pops-up "Do you want to save insert_filename_here.py before closing?", click "Yes"  --> nothing happens

Tested on 2 machines, same behavior.  If file has some previuos content, sometimes saving in IDLE works (not always).