Problem with adding labels in ggplot2

I apologize for not pasting a complete example, but the data-set is too large,
so I hope someone can help me just by description of symptoms. 

-snip-

I have solved the problem by introducing an artificial variable in the original
plot specification and plotting the data using the %+% operator, e.g.:

p.b4.idletime <- p.b4.generic.wg %+%
  within(b4.all.medians.8, { y <- v.idletime }) +
    ylab("Idle time (s)")