Various bits of what is known about busybox shells, in no particular order.

2007-04-21
hush: "sleep 5 | sleep 6" + Ctrl-Z + fg seems to work.
"rm -i" + Ctrl-C, "sleep 5" + Ctrl-Z still doesn't work
for SH_STANDALONE case :(

2007-04-21
hush: fixed non-backgrounding of "sleep 1 &" and totally broken
"sleep 1 | sleep 2 &". Noticed a bug where successive jobs
get numbers 1,2,3 even when job #1 has exited before job# 2 is started.
(bash reuses #1 in this case)

2007-04-21
hush: "sleep 1 | exit 3; echo $?" prints 0 because $? is substituted
_before_ pipe gets executed!! run_list_real() already has "pipe;echo"
parsed and handed to it for execution, so it sees "pipe"; "echo 0".

2007-04-21
hush: removed setsid() and made job control sort-of-sometimes-work.
Ctrl-C in "rm -i" works now except for SH_STANDALONE case.
"sleep 1 | exit 3" + "echo $?" works, "sleep 1 | exit 3; echo $?"
shows exitcode 0 (should be 3). "sleep 1 | sleep 2 &" fails horribly.

2007-04-14
lash, hush: both do setsid() and as a result don't have ctty!
Ctrl-C doesn't work for any child (try rm -i), etc...
lash: bare ">file" doesn't create a file (hush works)