What do you consider a glitch?
Glitches are incredibly hard to define in Mario Maker. It’s easy to say that anything you couldn’t do in the original games is probably a glitch. Of course, you must remember that Mario Maker has introduced many mechanics not seen in the originals. For that reason, things that may appear unintended by the creators could very well be a new technique.
A good rule of thumb is knowing the basic properties of Mario items. For example, the floor, ceiling and certain items are solid, so you shouldn’t be able to pass through them. If you need several special requirements to magically warp through a solid structure, it’s most likely a glitch. For the majority of players, what’s deemed a standard mechanic and what is probably intended should be obvious. If it’s not, it’s quite possible you’re dealing with a glitch.
Again, this is a very debatable subject, so no answer is going to be 100% correct. Until Nintendo informs us what we’re supposed to be able to do and what we’re not, we’re all in the dark.