I always prewash everything unless it is something that will be a wall hanging and probably never washed. I have had fabric bleed that is not even a batik - good quilting fabric from my LQS. I wash and then use Retayne if there is a problem. To use Retayne, you need to use very hot water (140 degrees or more). I read another thread talking about putting the fabric in a big pot on the stove with hot water and Retayne. It only takes a little Retayne in a pot of water.
Continued washing for several times may cause the fabric to look faded. The Retayne sets the dye.
Some of my friends think I am a bit fanatic about washing everything, but I can't see ruining my hard work because the fabric bled.