If you continue through floors 1-3 as normal, activating the boss gate switch on floor 2, and looping down from floor 3 to hit the floor 1 switch, you can then backtrack to floor 1 and take the secret portal to floor 3. Doing so opens a room on floor 3 with a bunch of treasure and a copy of the floor 2 gate switch. Pressing this extra switch allows you to drop the boss gate without using a gold key to reach the third floor's normal gate switch. Haven't tested if other routes (teleport up, go back down and hit switch 2 after using bonus switch 2, etc.) produce the same result, but presumably the boss gate is just counting to make sure >= 3 total act switches have been activated instead of matching specific floor 1 + floor 2 + floor 3 switches.
Free treasure and an expendable gold key to unlock something nice early, so not really a 'problem'. Based on the quantity of bonus treasure and the unlit floor tile in front of the boss gate I'm guessing it's unintentional.
Edit - The key at least doesn't follow you between acts. Oops!
