In his new autobiography, The Time of My Life, Swayze wrote: “We did have a few moments of friction when we were tired or after a long day of shooting.
“(Grey) seemed particularly emotional, sometimes bursting into tears if someone criticise her. Other times, she slipped into silly moods, forcing us to do scenes over and over again when she’d start laughing.
Here is Patrick Swayze talking about Jennifer, with some (minor, IMO) criticism of her: http://www.youtube.com/watch?v=b3Oc6PeTk9A