[jQuery] Selectors

Hi all,
I was using jQuery as usual, but i found someting unusual...
Is there any bug with selector ":last"?
For me the selector "#div_id div:last div:last" or "#div_id div:last
div:last div:last" isn't getting the div... but if i do a while and
get the .children( 'div:last' ) it works perfectly!
Some wild guesses?