This is indeed an example of why people pre-wash fabrics. I've had a couple projects ruined because I didn't pre-wash, so now I almost always pre-wash 99% of the time. Because we don't have our own washer/dryer, unless I have a lot of fabric to wash, I will often "pre-wash" by dipping the fabric in slightly warm water. I've been surprised by which fabrics bled and which didn't, like one fabric with a black background didn't bleed at all, but a medium green background fabric had to be washed out 4 times before it stopped bleeding. I know it's more work to pre-wash, then iron, but I usually do several yards at a time with my ironing board set up so that I can watch my favorite programs - it makes the time go by a little faster.