So after finally meeting the par time for 6-5, I saw Bandage Girl tripping out and nervously made my way toward her and opened up the Glitch Level. However, unlocking this level bugged the game.
After getting kicked out of the stage, this showed up:
The game did not award me the A+ for 6-5. Fearing the worst, I tried to enter the Glitch Level again and was able to. This shows up after completing it (note the Achievement Unlocked message):
I moved out of the square and... could not return to it.
This bug still lingers after restarting the game, preventing me from moving to the Glitch Level's square. I'm still not given the A+ for 6-5.