NPL v MPL query

[Chris Yoo]

Hello License Discuss group.

I am doing some research on open source licenses and would much appreciated
any assistance on the following query. 

I understand that the key difference between the Netscape Public License
(NPL) and the Mozilla Public License (MPL), was that the NPL reserved the
right on the part of Netscape to re-license code developed by third parties
under a proprietary or other license. While I understand the potential
reluctance of developers to contribute to the project due to this clause,
was this in breach of any of the OSD principles and thus the reason for it's
exclusion from the MPL? Thus, my question is:

Does the presence of the right of the Initial Contributor to relicense code
under another license make it not open source? 

My initial impression is that it does not contradict any of the principles.
I have tried to find similar discussion in the archives but have not been
able to find any - is it possible to search for keywords in the archive? 

Thank you in advance. 

Regards, 

Chris Yoo