[Dovecot] beta6 mdbox errors

[Mike Abbott]

Dovecot-2.0.beta6 sometimes terminates client connections and reports these errors:
Error: Corrupted dbox file /Volumes/Mail/joe/storage/m.1 (around offset=6216579): msg header has bad magic value
Error: Corrupted dbox file /Volumes/Mail/joe/storage/m.1 (around offset=6216579): uid=0 points to broken data at offset=6216579
Warning: mdbox /Volumes/Mail/joe/storage: rebuilding indexes

(I set mdbox_rotate_size = 200M.)

These did not appear with beta5.