How can you be 40% complete last week and still 40% complete this week? If you worked on it then the % complete should be increasing unless you have also increased the estimated remaining duration. If you haven't work on it since last week - then the task should be split.

In my opinion, no, you shouldn't be able to have 40% complete for several weeks running without either a split to show that you haven't worked on the task, or an increase in duration to show that you have worked on the task but you underestimated the initial duration.