When playing in Knuckles mode, some levels were dynamically redesigned to fit Knuckles gameplay. One of these levels are Launch Base Zone Act 1, where Knuckles can't never reach his path without a complete new level layout. The place where Knuckles throws a bomb at Sonic is totally gone. This is because the place were bombed before Knuckles game started.
Most of us see the acts in a level to be joined together, so where act 1 ends, act 2 continues. This is not the case. Act 1 will, as act 2 wrap and wrap and wrap until the screen coordinates reaches its maximum value. This can be seen while playing with debug, but never without it, OR that's what Sonic Team thought.
Bug 0004 description:
Knuckles sees a hole in the wall and runs into it just to meet another trap! Two mini bosses. Now Knuckles can jump over the hole, and climb up to Sonic's path. Because Knukles' bomb demo handled Sonic's boss by trigger Eggman into leaving the box and also locking the screen coordinates, Knuckles cannot trigger Sonic's boss at all. He will just pass through the box hall and the wrapping bug appears. He cannot get back into the main level again because the box hall is closed behind him. He's trapped forever!
Bug 0004 was never fixed!
The video of the bug (taken from the last version of Sonic 3 & Knuckles ever compiled) can be downloaded here:
More bugs/bug-fixes will be posted later. Post your comments!