Looks normal. Not a bug. Caused by a minor change in how the seed is used. As the 1.4.2 generation will consistently produce the same terrain with the same seed, it's definatly not a bug.
Commonly seem when the world name is reused. Old world didn't have time to delete and new one used the same folder name as the old which contained undeleted chunks. We're looking at user error.
Just updated Java, bug still exists with jre-7u45-windows-x64, and with jdk-7u45-windows-x64