Ouch, I had not realized that the ERC does not check for this! Must have got lucky and never forgotten a power "gate" so far.
This is quite annoying, since it overlooks an error which is somewhat easy to make, and will result in a non-working PCB. (Well, at least it will typically be fixable with bodge wires...) Too bad that this apparently did not make the cut for 6.0, given that the problem persists in 5.99.