Small issue. If you teleport out of Dr Wily's area, the music keeps playing, even when you change area and other music is playing. You need to actually go back to Dr Wily's area and complete it to stop the music.
It happened when my save was at Dr Wily, and I went left to complete the area, did something near the start and pressed R. So then I pressed M to go back to the start and the music didn't stop.
EDIT: I've just had it happen again in the water area under the main screen, simply by warping to the start.
EDIT 2: I've just lost my save file. I was doing the Cherry challenge and I just got into the lift that slowly goes downwards. I faced left and shot the save without leaving the lift and my save was completely corrupted.
EDIT 3: How do you get to the bottom left room in the tutorial area? Never mind.
EDIT 4: Minor glitch. Try collecting a rainbow ball and leaving the room before the timer runs out. Your next shot will be a special shot and there's no time limit. Also, press R from the achievement menu and it'll go back to the game. It went to File 1 for me, I don't know if it's always 1 or your most recent file.
Yay, achievements 1, 4, 5 and 13. 100% on Medium. I want to try for other achievements but the lack of clues makes it awkward. I think I'll try playing on harder difficulties.