I did some testing with WebSphere Liberty 8.5.5, and if I'm not mistaken it looks like it bundles MyFaces 2.0.3 or 2.0.4. The 2.0.3 implementation is from 13 December 2010 and contains quite a few bugs and performance issues.
Why does Liberty bundle such a rather old version?
Edit: I found this message saying it bundles 2.0.5: https://www.ibm.com/developerworks/community/forums/html/topic?id=2010a28b-37ef-44b6-aa3b-3a4f9f2095fa&ps=25
I couldn't however find the key "org.apache.myfaces.FLASH_SCOPE_DISABLED" in META-INF / myfaces-metadata.xml, which was introduced in MyFaces 2.0.5. At any length, 2.0.5 is from 5 April 2011 which is still rather old.
Why not bundle a relative recent version from the 2.1.x series and support JSF 2.1 at the API level instead of 2.0? Nearly all other app servers (JBoss, GlassFish, WebLogic, TomEE, etc do that as well).