This topic is very interesting. I think this is the most common problem while working in team. I have experienced this situation many times due to lack of communication, delay in replying and most important when the team members rely on each other to get things done. While working in company, it is not possible to rely on each other completely because everyone assigned to do his/her own task and expect to finish in timely manner. WBS is created for a reason, for example help explains project more in details, assigning responsibilities, and realizing the time, cost and risk associate with the project.