iOS 5: renderInContext erase context

My app is fully working on ios4. I incrementely drawing over the context. I m using renderInContext before drawing on the layer to keep the previous drawing. In iOS 5, the new draw which is called with drawInRect erase the context with the full rect. For example if i have a full colored square in the context and i m drawing a line on it with drawrect开发者_JS百科, i have à transparent square around the line in the square... Do you know how to avoid this and having only the Line over the square...?? Like it is in ios4! Thank you

I changed the way of drawing. Using an image and drawing into it