Or is this a bug?

What's the difference? Is it where the log is located? If it is, it's because of your pet's level. The level or your explore pet changes the size of the island you're exploring on (the higher the level, the larger the island). Therefore, the location of the explore log changes to save space and not stretch the screen.

Oh! Yes, that's my first pet to get over level 10. I guess I didn't even notice the island size. Well that makes sense. I still prefer it to the left (now it goes off my screen and I can't see the most recent events without scrolling), but good to know that's normal.