After I asked that question about Mann, I went and read tons of reviews, and that issue came up time and time again, whether the critic loved it or didn't. Even people explaining it aren't sure, because the movie didn't really tell you exactly what's going on, especially with a character we know little about.
And as far as the exposition in this movie goes, it really didn't feel that natural. Why would NASA scientist/pilots need a refreshers on Relativity every so often? Basically, the exposition that was there was too heavy handed, and when it was actually needed, it was completely absent. Exposition is fine, but it seems Nolan has a hard time juggling it more than most directors. Eh, but what do I know? I'm too stupid to know what's going on. I miss everything in movies.