strange missing value message from geom_point : I have a really strange missing values message which is not reproducible and I also can't find the problem. Any suggestion? 
Once I get the warning, once not, and by counting NAs, I don't find it.

    > ggplot(jnk, aes(x=Experiment, y=Log2Intensity)) + 
    +     geom_boxplot(outlier.shape = NA) +
    +     geom_point(aes(color=imputed), 
    +                position=position_jitter(width=.4), 
    +                alpha=.5) + #scatter dots, fill if imputed
    +     scale_color_manual('Imputed', values = c(`TRUE`='blue', `FALSE`='orange')) +
    +     scale_y_continuous(limits=range_intensities) +
    +     facet_wrap(~ my_label, ncol = 10, nrow=5)
    > ggplot(jnk, aes(x=Experiment, y=Log2Intensity)) + 
    +     geom_boxplot(outlier.shape = NA) +
    +     geom_point(aes(color=imputed), 
    +                position=position_jitter(width=.4), 
    +                alpha=.5) + #scatter dots, fill if imputed
    +     scale_color_manual('Imputed', values = c(`TRUE`='blue', `FALSE`='orange')) +
    +     scale_y_continuous(limits=range_intensities) +
    +     facet_wrap(~ my_label, ncol = 10, nrow=5)
    Warning message:
    Removed 1 rows containing missing values (geom_point). 
    > apply(jnk, 2, function(x) sum(is.na(x)))
         my_label   Protein.IDs    Experiment     replicate       imputed Log2Intensity          page 
                0             0             0             0             0             0             0 