strange behavior of R

Hi
I observed an interesting behavior of R. Can you find where is the  
bug, or
it is not a bug but made deliberately.
- Hide quoted text -

arr = c();                        #defined the empty array
a= c("x1", "x2");
b = c("y1", "y2");
arr = rbind(arr,a);            #row bind the first character array -a
arr = rbind(arr,b);            # row bind the second character  
array-b

Everything ok upto this point, arr content is displayed as follows

arr

 [,1] [,2]
a "x1" "x2"
b "y1" "y2"

Now I delete any row:
arr = arr[-1,];

The value of arr is :

arr

[1] "y1" "y2"

Problem: I want to access the first row now using:

arr[1, ]

Error in arr[1, 1] : incorrect number of dimensions