I've written a test case in Python to reproduce this bug. It could easily be turned into a DEP 8 automatic package test.
The output looks like this: q:Exit -:PrevPg <Space>:NextPg v:View Attachm. d:Del r:Reply j:Next ?:Help m0 0| 1 N Oct 10 test@test ( 24) test m1 0|-*-Mutt: =tmppaeZ8M [Msgs:1 2.3K]---(threads/date)------------(all)--- m2 0|wwwwwwww ggggg lllllll u aaaaaaaaa llllllll aaaaa m3 0|ffffffffff x aaaaaa yyyy fffff aaa lllll ggg fffff h vvvvvv qq m4 0|+zzzzzzzzz dddd ssssssss yyyyy m5 0|rrrr ppppppppp wwwwww p gggggggg kk oooooooo rrrr llllll uuuuuu kkkkk m6 0|+a ssssssssss pppp eeeeee zzzzzzzz ooooooooo gggggg m7 0|ppppp hhhhhh y uuuuuuuuu xxxxxxxx vvvvvv ooooo bbbbbbbbb oo nnnnn jjjj +ooooooo ppppp aaa eeeeee wwwwwwww uuuuuuuuu ggggggggg r a gg qqqq bb nn hhhhhhhh llll m kkkkk ee xxxxxx fffffff v aa ss sssssss +ooo zzzzzzzz fffffff kkkkkk iiiiiii bbb zzzzzzzzz hhhhhhhhh iiiiiiiiii ttttt g w m12 0|+vvvvvvvvvv oo wwwwwwwwww m13 0|nnnn jjj rrrrr ff rrr mmmm wwwwwwwww aaa iiiiiiiiii uuuu fffffff m14 0|+vvvvvvvvvv iiiiiiiii rrrrr zzz s m15 0|xxx ttttttt vvvv iii wwwwwww yyyyyyyyy dddddd m16 0|b wwwwwwww vvvv pppppppp jjjjjj f m17 0|xxxxxx yyyyy hhhhhhhh v r ccccccccc bbb zzzzz dd m18 0|tt xxxx zzzzzzzzzz hhh mm q aaaaaaaaaa hhhhhh m19 0|i xxxxxxxxxx zz fffffff zzzzzz rrrrrrr gggggg hhh ccc zzzzz qqqqqqq m20 0|+yyyy m21 0|-N - 1/1: test@test test -- (41%) You can see a gap in the list of mailboxes in the sidebar. Here is the code. The python-pyte and python-pexpect packages need to be installed. import pyte import pexpect from random import seed, randint from tempfile import NamedTemporaryFile import os def write_muttrc(f): f.write(''' set folder=/tmp set sidebar_visible set sidebar_width=10 set pager_index_lines=4 mailboxes ''') for i in range(30): f.write(' =m{}'.format(i)) def write_mbox(f): for line in ('From test@test Sat Oct 10 10:00:00 2015', 'Subject: test', 'To: test@test', 'From: test@test', ''): print >> f, line seed(1) for i in range(25): print >> f, ' '.join(chr(ord('a') + randint(0, 25)) * randint(1, 10) for i in range(randint(5, 20))) def run_mutt(muttrc, mbox): stream = pyte.ByteStream() screen = pyte.Screen(80, 24) stream.attach(screen) mutt = pexpect.spawn('/usr/bin/mutt-patched', ['-F', muttrc, '-f', mbox]) mutt.send('\n' * 5) while True: try: buf = mutt.read_nonblocking(mutt.maxread, timeout=1) except pexpect.TIMEOUT: break stream.feed(buf) mutt.send('q') return screen def main(): f = NamedTemporaryFile(delete=False) muttrc = f.name write_muttrc(f) f.close() f = NamedTemporaryFile(delete=False) mbox = f.name write_mbox(f) f.close() for line in run_mutt(muttrc, mbox).display: print line os.remove(muttrc) os.remove(mbox) if __name__ == '__main__': main()