OS: Windows 10 Pro
Version: 1909
OS Build: 18363.657

Python 2.7.17 and 3.8.1 were installed from https://www.python.org/downloads/ using the Windows x86-64 executable installer (3.8.1) and Windows x86-64 MSI installer (2.7.17)

Both line numbers and code context are not present

To reproduce:
1) Position cursor at the start of a line of text
2) Type Shift+down arrow (to select line of text)
3) Type Ctrl+c
4) Type Alt+g (IDLE) or Ctrl+g (Notepad, Notepad++)
5) Enter line number (for example below line number = 2)
6) Type Enter
7) Type Ctrl+v


Example initial text:
# This is line 1

# additional line
# This is a line I wish to duplicate
# another additional line


Resulting text in IDLE:
# This is line 1
# This is a line I wish to duplicate

# additional line
# another additional line


Resulting text in Notepad and Notepad++:
# This is line 1
# This is a line I wish to duplicate

# additional line
# This is a line I wish to duplicate
# another additional line


My workaround in IDLE is to add a step between #6 and #7 above, where I mouse click at the desired paste location