ess-S-quit-kill-buffers-p is not respected

[ywwry66]

To reproduce:

1. Set ess-S-quit-kill-buffers-p to ask
2. Start an R session by M-x R
3. Quit R by calling ess-quit.
4. Answer y to the prompt "Delete all buffers associated with process R?"
5. Answer n to the prompt "Save workspace image?"

The value ask does trigger the prompt, but it does not kill any buffers associated with R. Setting ess-S-quit-kill-buffers-p to t does not kill the buffers either. I have also tried setq inferior-R-args "--no-save", and the result is the same.