No that's completely how bugs work. I have done a little bit of coding myself, in a C++ like format, and even when I copy/pasted code into it from another source, it wouldn't work. Try a game from scratch, use the same code? Worked flawlessly. Bugs are weird. Sometimes all it takes is a single extra space somewhere, a inproper indent, an extra character, etc.
Or sometimes code just freaks out. It's weird like that.
And no, that doesn't paint a picture. That just proves my point: bugs aren't always something that happens. Sometimes they do, sometimes they don't. And also, they might happen, you just might not notice it, or may not realize it wasn't supposed to work that way in the first place. Is every bug as easy to spot as, say, the randomly flying mammoths, or the "being punched to the moon" that happens in Skyrim? Nope. Sometimes a bug is a simple, little thing you don't notice.