I have never seen a locking tab on Front Panel wiring connections on the motherboard
I think I know what your referring to, like on the power supply connector that plugs into the mother board. We're talking about a little tab that holds the metal contact in the plastic shell. If you lift it slightly you can pull the wire and the contact and all comes out. You'll be left with the wire and the metal contact that's crimped to its end in one hand, and the plastic shell in the other.
But this is about the case's front panel wires that connect to the motherboard's Front Panel I/O, not power supply cables that connect to the motherboard's power connectors. So I agree with caperjack and there should NOT be any locking tabs. If you reverse the connectors from the case's front panel, no harm will be done. The power and reset buttons will still work and at most, the LED lights for power and HD activity will not light.
If there are locking tabs, then someone has the cables mixed up.