Sonic the Hedgehog 4 bug list
From Sonic Retro
This is the bug list for Sonic the Hedgehog 4.
Getting stuck in loops
The chief bug is getting caught standing on the side of loops. An issue similar to this occurred in certain parts of Chemical Plant Zone in Sonic 2 (and Knuckles in Sonic 2) where you could get stuck behind the loop apparatus if you got out of the spin dash at the wrong time. Its unknown at this time as to what causes the glitch in Sonic 4. Here is a YouTube video of this glitch in action (in Splash Hill Zone).
iPhone Version: Swiping on level select advances to wrong level
Swiping left and right on the iPhone version of the game causes the currently selected level to advance in the opposite direction.