Other quirks apparently caused by this bug:

msvcrt.getch() does not block and wait for a keypress in IDLE.  Returns immediately with b'\xff'.

Some of the suggested usage in the manual for sys.stdin does not work under IDLE.  E.g. sys.stdin.detach() doesn't work in IDLE.  On this last point, the manual has a caveat in the last line of the sys.stdin description that could exonerate it.  Regardless, the behavior is inconsistent and makes for awkward UI when using IDLE.