Mentor trying to be first author? I was on an internship with professor A at University B in China. We were working on a computer science project. During the internship I implemented professor A's idea and got some results. Three weeks ago I finished a paper draft and left University B for a new internship. Me and professor A were planning to submit the paper draft to a conference (deadline: May 20). 

Until yesterday (May 17), the order of authors was: me, professor A, other students &amp; collaborators in the lab... And professor A had no objection with that. However, last night I received an email from him. He said he wants to be the first author... His reason was for intellectual properties and patent issues. My understanding is that because I was merely an intern at University B, if the first author was me, it would cause IP troubles for him?

I feel deceived. But, should I feel like this? I was counting on a first-author paper because I'm planning to apply for a PhD program in the US. One paper may not mean a lot to someone who's published a lot. But for someone who hasn't published yet, it means something.

Looking on the Internet, I found something that might explain professor A's motivations: 
In China specifically, corresponding authors are often underappreciated by universities and research institues. This might be the case for University B. Given professor A is relatively young, he may want first authorship for promotion.

Summary of my questions:


Should I go discuss with professor A and try to persuade him to let me be the first author?
If I want to apply for a PhD program in the US, would being the first author be more helpful or being the second author is as well helpful?


Edit:


My affiliation for the paper has always been University B. I didn't mention my current university or internship in any sense.
I emailed back to professor A yesterday, saying I think I should be the first author, because I did most of the work; because the idea was originated from him he should be the corresponding author. He replied this morning, saying he agree with what I said. He explained that because I was doing an internship in his lab and not a student of University B, putting me as the first author could cause IP and patent troubles for University B... So this problem is fixed now.
I don't really understand what the motivation here for the professor is. Since you did all of the work for this paper at University B, you should not list your new affiliation (whether it's an internship or another school) as an "active" affiliation for this paper. It can be listed as a "current address," but not as an active address for this paper. In that way, the professor still gets credit for your work, with your affiliation showing as being part of his group. (I suspect that the professor's concern is that, if you are at another institution and list that as your address, he won't get credit for his work.)

Another issue is that if you are not going to present the paper at the conference, he may have felt it was in his interests to list himself as a first author. How appropriate this is I have to leave to the CS community to judge. 

In general, however, the first author should be the person who has made the largest contributions to both the research and the writing of the paper. Deviations from this need to have a very good foundation.