Yes, I would say it’s undefined. If we translate the standardese to pseudo-code:
if (typeof(E1) == unsigned integral) value = E1 * 2^E2 % blah blah; else if (typeof(E1) == signed integral && E1 >= 0 && representable(E1 * 2^E2)) value = E1 * 2^E2; else value = undefined;
I’d say the reason why they’re explicit about the right-hand operand and not about the left-hand one is that the paragrpah you quote (the one with the right-hand operand case) applies to both left and right shifts.
For the left-hand operand, the ruling differs. Left-shifting a negative is undefined, right-shifting it is implementation-defined.