Pasting multiple lines at once with typeahead

The bracketed paste to paste a bunch of lines to a single prompt doesn't seem to work properly when using typeahead. For example, copy the following lines

a
b
c

then run the following.

import time
from prompt_toolkit import prompt

time.sleep(1)

while True:
    prompt('> ')

If you paste the lines after the > prompt appears, they all paste into one prompt:

> a
b
c
>

But if you paste them before the prompt appears, they each get their own prompt:

> a
> b
> c
>

Start by running the supplied Python prompt loop and reproduce the difference between pasting after the prompt appears and pasting during typeahead. Trace the prompt_toolkit code handling bracketed paste and queued input; done means multiline paste produces the intended prompt behavior in both timing cases, with regression coverage for the example.