Hi Vedran, that seems to now be the default behavior, regardless of previous installs (my 3.6 was a clean install, and it's still nested).  Kind of a pain if you want to edit with IDLE frequently.

While we wait for a more integrated solution, the hackish way to restore desired behavior is to run a .bat file containing:

REG DELETE "HKEY_CLASSES_ROOT\Python.File\shell\editwithidle"

Then run a .reg file (also just a text file with altered extension so windows knows what to do with it) with:

Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\Python.File\shell\Edit with IDLE 3.6\command]
@="\"C:\\Program Files\\Python36\\pythonw.exe\" -m idlelib \"%L\" %*"