If your being called by J/8 after a substancial raise that player is horribly bad or is chipbuilding at a re-buy table.
Other posters here have it right your A/A is going to be cracked 20% of the time under normal circumstances, but in a rebuy period with one or more maniac chipbuilders .... well those ain't normal circumstances. I haven't run the math but they will be cracked more than 20%.
A lot of new players come into re-buy tournaments and are flabbergasted at the tactic of chipbuilding. There are players, (usually better than average in skill) that will for the first 3/4 of the re-buy peirod go all-in with any 2 cards and not care if they win or lose, they just keep re-buying and going all-in so they can build a large mass of chips at the table.
Then around half way or 3/4 way in re-buy, just before the add-on break they will either get fortunate and aquire a big stack or tighten up and begin to collect as many chips as they can. After add-on break they have a chip advantage on about 3/4 of the field.
It's a crazy tactical strategy but there are players with a lot of cash who do this often to gain advantage where they can. I don't know if this is whats happening in your case, but that's the first thing that popped into my mind when I read your original post.
For anyone who's never experianced chipbuilding in re-buy tournaments don't panic. Set a limit, 2 or 3 re-buys plus add-on, play like a ROCK during the re-buy peirod only go all-in with A/A, K/K, Q/Q, A/K and if your brave enough ANY pocket pair.
Your chances will be 50/50 of going into the main event (after re-buy) with a better than average stack or with the minimum. Re-buy peirod is often just a luck fest and luck is fickle, you can be just as lucky as anyone else during this time or conversely unlucky.
I've seen players spend over 400 bucks in the 10 dollar re-buys, to someone who is building a
bankroll from scratch that looks CRAZY. But believe it or not there is a method to their madness, take advantage if you can, but beware it can cost you plenty. On the other hand it can also be a great advantage and lead into the main game.