My wife is in the same position. Her OWP expires March 19th, the day her old passport expires. The fact that you have an inland application in process does not give you legal status. You need to renew your OWP before the deadline. Make certain they have it in their office before the date of expiry. You will then be on implied status, legally able to work, under the same conditions stipulated on your OWP, while they process the application.
What I am unclear about, however, is if when submitting the renewal if we somehow need to connect it with the PR application. Perhaps, an expert can tell us, otherwise we'll need to get on the phone and ask CIC. My wife wants to include a student permit application with it. Anybody have any experience with this? She will be giving birth around end of June and would simply like to take a course in September. As a new mother, I am sure that is the most she could handle. So I'm not sure if we need to prove sufficient income as one would normally for a student permit.