Just have to say the wrong thing i did, i had pre-printed squares that I bought and what did I do? I washed them of course. well the lovely blue lines went away. I contacted the company i got them from and claimed to be dumb (well I was) but also told them they should state that the squares should not be pre-washed. i pre-wash all fabrics! they sent me more. nice company and they never put that statement in. oh well, hopefully no one else was just as dumb as me.
so far, i've not pre-washed my fusible batting!