[R] lattice: horizontal alignment of labels in key

[Thomas Zumbrunn]

Dear R users

I have problems horizontally aligning labels in keys of lattice plots when the 
labels make use of plotmath. Here's a self-contained example:

dat <- data.frame(x = rnorm(10),
                  y = rnorm(10),
                  z = factor(rep(c("a", "b"), each = 5)))
xyplot(y ~ x, dat, groups = z,
       auto.key = list(columns = 2,
         text = c(expression(plain("alright")),
           expression(italic("too low")))))

It seems like the grid object which the lattice function creates from the key 
arguments has different heights for the two labels since the second label does 
not stretch over the baseline.

Any ideas how I could circumvent the problem (other than manipulating the key 
grob)?

Best wishes
Thomas Zumbrunn