Example of the bug:
tt <- expression(paste("test loooooooooooooooooooooooooooooooooooooooooooooo(% of 360" *degree,")"))
#Now please resize the window to a smaller window to see how the text in ylab disappears
#(but not the xlab or title.)
#This also seems to affect vertical rotated expressions:
#At least on windows.
#On Linux (so Barry wrote), all the rotated texts seems to disappear.
# I wasn't able to find reference to this when searching, but maybe I failed in looking.
# Here is my session info:
R version 2.11.1 (2010-05-31)
 LC_COLLATE=Hebrew_Israel.1255 LC_CTYPE=Hebrew_Israel.1255 LC_MONETARY=Hebrew_Israel.1255 LC_NUMERIC=C
attached base packages:
 stats4 splines stats graphics grDevices utils datasets methods base
other attached packages:
 multcomp_1.1-6 coin_1.0-11 modeltools_0.2-16 mvtnorm_0.9-9 survival_2.35-8 reshape_0.8.3 monoProc_1.0-6 stringr_0.3
 R2PPT_1.0 rcom_2.2-1 rscproxy_1.3-1 rootSolve_1.5 plyr_1.2 zoo_1.6-2 colorspace_1.0-1
loaded via a namespace (and not attached):
 grid_2.11.1 lattice_0.18-8 tools_2.11.1
It's a bug alright. Fix in r53057