It took me a while to experience this enough to understand what was happening. It was driving me crazy. I draw 2D floor plans before I start modeling and apply the traditional wood grain hatch to my walls. I notice that sometimes when I am making corrections to walls and hatch the hatch would disappear and turn to a white background. What is really happening, I discovered, is that there is a bug and sometimes this action changes the current style to the default style which does not display the hatch. Now that I know, I simply change the style back to Construction Documents Style and all is well but the devs and users need to know what is happening. Styles should not change on their own. They should remain as the user has assigned.