Various bits of what is known about busybox shells, in no particular order.
+2008-02-14
+ash: does not restore tty pgrp if killed by HUP. Symptom: Midnight Commander
+is backgrounded if you started ash under it, and then killed it with HUP.
+
+2007-11-23
+hush: fixed bogus glob handling; fixed exec <"$1"; added test and echo builtins
+
+2007-06-13
+hush: exec <"$1" doesn't do parameter subst
+
+2007-05-24
+hush: environment-related memory leak plugged, with net code size
+decrease.
+
+2007-05-24
+hush: '( echo ${name )' will show syntax error message, but prompt
+doesn't return (need to press <enter>). Pressing Ctrl-C, <enter>,
+'( echo ${name )' again, Ctrl-C segfaults.
+
2007-05-21
hush: environment cannot be handled by libc routines as they are leaky
(by API design and thus unfixable): hush will leak memory in this script,