Yep that's right there will always be bugs. Even though my retro pixel RPG 'A Dungeon Horror Deed' have been play tested again and again I found a bug the other day. It goes to show that even relatively simple games, are complex. But it was easy to fix fortunately, because I have focused on maintenance when designing the game engine.
When you create software, you create a huge amount of paths and combinations of paths through the code that even the most intensive automated and manual testing never will ensure to be a 100% error free.
So what seems to be robust and good code can come back and bite you in the ass. But I fixed it and that feels good