Actually, it was also likely to be a model bug. I've seen it done and done it myself, and it's reproducable for those of you who wantr to give it a go.
Using Goku, transform once you reach the required power level.
Then, press both ascend and descend at the same time. Goku will begin going super saiyan, but will keep his Ssj Model.
While he's ascending, press the descend key to stop him. As far as the code, attacks, ki anbd power level know, You'll be normal Goku, but you will retain the Ssj Goku Model.
You can now press ascend at your will, and it appears as if Goku the Super Saiyan, is going Super Saiyan again. I hope that clears things up a little.
Give it a try guys, it doesn't provide any advantage, but it is fun to play with. As for characters other than goku, it has marginal effectiveness.