All this means is that the Container *may* use
Java serialization to passivate the bean, so the spec is warning the developer that if a variables is marked "transient", you cannot expect the value to be maintained. In other words, you can assume that passivation might serialize your bean, and therefore transient variables are lost.
But then of course there is the *other* little note that warns that since it might NOT be serialization, the transient value won't necessarily be reset to its default value... but that's a different issue.
The thing to remember is the list of *states* your variables are allowed to be in by the end of ejbPassivate() (for a stateFUL session bean). You're required to know this for the exam... to know, for example, that the Container MUST successfully passivate a reference to a SessionContext even if the SessionContext implementation class turned out NOT to be serializable... doesn't matter because it is on the Container's MUST BE PASSIVATED SUCCESSFULLY list.
cheers,
Kathy