R would not quit (bug?) (PR#6600)

Hello.

I am not sure if this is a bug.

I loaded into R a very large matrix, around 600,000 X 30 integers.  My 
machine has 2G ram.

After trying to write.table a modification of this matrix, R generated 
some sort of malloc error.

Then,

Error: vector memory exhausted (limit reached?)
 > q()
Save workspace image? [y/n/c]: n
*** malloc: vm_allocate(size=8421376) failed (error code=3)
*** malloc[14681]: error: Can't allocate region
Error: vector memory exhausted (limit reached?)
 >

Eventually I just killed the R session directly.

Michael