Brushes stay hard after cleaning

I use testors enamel paints and thinner from Lowes that supposely is more evironmentally safer and comes in a plastic bottle. I generally wipe the brushes on a rag and thinner until they are clean and then wash them in water with soap, then form their shape with my finger tips. When the brushes dry, they are kind of hard and have to soften the brushes by slowly bending the bristles. Is this normal?

Source: http://cs.scaleautomag.com/SCACS/forums/thread/987959.aspx

Johnny Boyd David Brabham Gary Brabham Jack Brabham† Bill Brack Ernesto Brambilla Vittorio Brambilla Toni Branca Gianfranco Brancatelli Eric Brandon