I've tried to check the source code of IDLE in search of chained comparisons without parenthesis (like the example I showed and the bug with the mouse wheel). I couldn't find something important.

Then I wrote in a file the following code:

import tkinter

root = tkinter.Tk()

text = tkinter.Text(root)
vbar = tkinter.Scrollbar(root)

vbar.pack(side=tkinter.RIGHT, fill=tkinter.Y)
text.pack(side=tkinter.LEFT, fill=tkinter.BOTH)

text.config(yscrollcommand=vbar.set)
vbar.config(command=text.yview)

lines = ['This is the line number %d.\n' % i for i in range(200)]
text.insert(tkinter.END, ''.join(lines))

In both Python 3.6 and 3.7 with Tk 8.6.8 on macOS 10.13, click-and-drag on the upper half of the scrollbar slider has no effect (the slider sticks at the top), like in the bugs #1 and #3. I strongly suspect a tkinter problem, as the equivalent Tcl/Tk code functions well. Click-and-drag in the lower half of the slider functions (in my code and IDLE) for me. Can someone reproduce this?