When Sonic or Knuckles reaches the goal as Super Sonic/Knuckles, they revert back to their original form. The player can transform into Super Sonic/Knuckles again in a brief window of time before the Act Clear results screen appears, but this causes a glitch forcing Sonic/Knuckles to quickly revert to their original form, trapping them in midair in an endless walking cycle as the current stage's music continues to loop, and leaving you stuck without advancing to the next stage as the Act Clear results screen will not appear.

This glitch can also be performed after finishing a fight with Dr. Robotnik, when the player frees the Animals from the Capsule and then transforms into Super Sonic/Knuckles immediately after. You will still be trapped in midair, but unlike regular Acts, the Act Clear results screen will appear and allow you to advance to the next stage normally.
Contributed by ProtoSnake