The way that loading it crosswise causes it to shift into a double half hitch, turning from a "hold fast" knot to a slipknot... That's funky behavior and should disqualify it from being among the first few knots people learn. If you're using it for its advertised purpose, it's downright dangerous, and the square/granny confusion is just needless pain to discourage a newbie.
If you wanna tie two ropes together and have a less finicky experience, use a fisherman's knot. Which is basically a pair of overhands, each around the other rope.
It's a much more reliable knot for trying two ropes together, lacks the annoying gotchas of the square knot, and for a long list of reasons I won't bore you with here it is a better foundation for learning other knots. (It's no good for drawstrings though, too reliable, no quick release).