Most of the PhD applicants have probably gone through the process of writing, revising and editing the research proposal based on the supervisor's/prospective supervisor's comments. I finished the initial version of my proposal in December and sent it to my prospective supervisor, who got back to me saying that the proposal was good to go. I only submitted my application several weeks ago (I'm working full-time, so it took me some time to get in touch with the referees from my BA/MSc schools), and then, last week, I received a very confusing e-mail from the programme administrator. In short, I was told that my potential supervisor found my proposal underdeveloped and wanted me to revise it. He did mention that the choice of the research problem was good, interesting even, though. Not only did I find this really confusing given that the professor seemed to have already approved the proposal, but I was also advised that he was too busy to provide any detailed advice. The problem is, I'm not sure what I could/should change in my paper, and I wouldn't want to take a shot in the dark here. I was thinking of sending him a brief e-mail with just a couple of sentences describing my ideas on how to change the proposal and ask if he approves - would that make any sense? I also have to say that I've applied to two other universities. For one of them, I had to completely re-focus my research question/problem, following the potential supervisor's comments and suggestions. I could probably use the same approach for the proposal I have to revise, but I'm not sure it would fit in with that professor's research interests.
I'm really just looking for some level-headed advice here, so I'd be grateful for any comments - thanks!