Seen this error a few times from dovecot-1.1.14, Mac OS X, 64-bit
Intel. Pretty sure NFS was not used.

Panic: IMAP(user): file index-sync.c: line 39
(index_mailbox_set_recent_uid): assertion failed:
seq_range_exists(&ibox->recent_flags, uid)

The backtrace is:

0 libSystem.B.dylib 0x00007fff85025166 __kill + 10 1 libSystem.B.dylib 0x00007fff850a80e0 abort + 83 2 imap 0x0000000100069f3e
default_fatal_finish + 70 3 imap 0x0000000100069f8c
i_syslog_fatal_handler + 0 4 imap 0x00000001000696eb i_info + 0 5 imap 0x000000010003b86b
index_mailbox_set_recent_uid + 74 6 imap 0x000000010003b8cb
index_mailbox_set_recent_seq + 58 7 imap 0x0000000100018f5d
maildir_sync_index + 2163 8 imap 0x0000000100017ba5
maildir_sync_context + 662 9 imap 0x0000000100017d8e
maildir_storage_sync_init + 104 10 imap 0x000000010000c037 imap_sync_init +
132 11 imap 0x000000010000c289 cmd_sync_delayed

• 477 12 imap 0x0000000100006ae8
  client_handle_input + 409 13 imap 0x0000000100006bc2 client_input + 148 14 imap 0x0000000100070f83
  io_loop_handler_run + 272 15 imap 0x0000000100070348 io_loop_run + 55 16 imap 0x000000010000db95 main + 1635 17 imap 0x0000000100001010 start + 52