Wow, very interesting! That sounds like a somewhat significant change, and I wonder how much stuff will be broken by it.

Although interestingly somehow I'm still seeing the old behavior in Debian Buster with glibc 2.28 with python3.

    import sys
    while True:
        b = sys.stdin.read(1)
        print(repr(b))

With old glibc with both python2 and python3 the EOF isn't sticky (as expected). With 2.28 with python2 the EOF is sticky (like you said). With 2.28 with python3 it's not sticky for some reason.