[R] Infinite recursion error that I don't understand

[Bert Gunter]

> sessionInfo()
R version 2.6.1 Patched (2007-12-03 r43574) 
i386-pc-mingw32 

locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
States.1252;LC_MONETARY=English_United
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252

attached base packages:
[1] grDevices datasets  stats     graphics  grid      tcltk     utils    
[8] methods   base     

## ... + other packages..
  
> z <- rep(Sys.time(),5)
> data.frame(z)
                    z
1 2008-01-03 10:19:43
2 2008-01-03 10:19:43
3 2008-01-03 10:19:43
4 2008-01-03 10:19:43
5 2008-01-03 10:19:43

> data.frame(I(z))
Error: evaluation nested too deeply: infinite recursion /
options(expressions=)?

## I don't have a clue. Any words of wisdom would be appreciated.

Bert Gunter
Genentech