I looked up those two papers: "Python CS1 as Preparation for C++ CS2": http://www.cse.msu.edu/~enbody/fp039-enbody-revised.pdf and "Performance of Python CS1 Students in Mid-Level Non-Python CS Courses": http://dl.acm.org/citation.cfm?id=1734437 (email me if you'd like a copy, it's behind the ACM paywall).

Neither of your claims is supported by either paper. Rather, they seem to support my claim: starting language isn't a predictor of success.

Conclusions from the first paper: When final exams were compared for a CS2 course offered before the Python transition with a course after the transition no statistical difference was found. The first CS2 course after the transition contained a mixture of Python-prepared and non-Python prepared students. There was no statistical difference in the performance between those two student groups.

Conclusions from the second paper: We conclude that starting students with Python has not had a negative impact within a C++ based curriculum. It would have been nice to conclude that the Python students did better in these courses, but the evidence does not appear to support that hypothesis.

With that said, I do agree with the authors that exposure to more languages, environments and tools is a good thing, and for that reason, I'd prefer using Python, then switching to C++.