When you create WildFly servers you can configure which JVM it should use.
Eclipse actually should be doing this all based on your default JVM and settings so if you can outline what setup you are actually running we might be able to figure out what is going wrong.
i.e. I don't run the IDE with Java 8 and I don't see these issues....are you by any chance running the IDE with Java 8 ?
It seems to happen only if I import an EAR file into projects. On creating a new project, the java facet is 1.7 as expected.
Do you think this is an WTP bug?
jdt, wtp or m2-wtp bug - depending on what kind of setup and import you got.