• Permissive licenses (MIT, Apache) carry no restrictions on re-licensing when blending source code for distribution.
• Elastic licenses (Eclipse) require that the original source code and its direct derivatives remain under the original licenses, whereas any code that is added can be under any license(s).
• Unified licenses (GPL, AGPL) require consistent licensing of software at the program level when blending code for distribution.

Source: Potvin, J. 2012. "Flow Licensing and Contracting: Applied Intellectual Resource Economics in the Canadian Public Sector". In: Mark Perry & Brian Fitzgerald (eds). 2012. Knowledge Policy for the 21st Century: A Legal Perspective. Irwin Law Publishers: http://www.irwinlaw.com/pages/knowledge-policy-for-the-21st-century--a-legal-perspective