>The Pokémon Day Care is run by an old couple that look after Trainers' Pokémon while they are away. If you leave a Pokémon with them, you may return to find that it had leveled up. The old woman will only accept one Pokémon at a time, but return here after meeting her husband in Nimbasa City, and you'll be able to leave up to two Pokémon at once. If the two Pokémon are compatible, the old couple may discover an Egg!
Not sure if that's what you're talking about. Not a glitch if that's what you meant, though.
P.S. Nimbasa City is where the 4th gym is.