[Dovecot] dovecot.index.cache

[Fintec]

Hopefully someone can explain/help me with the dovecot.index.cache
file. 

I am wanting to move a dovecot server (v1.0b7) onto a new box running
the same version (1.0b7) of dovecot. To do this I rsync'd the maildir
files to the new server but when I logged into the new machine through
IMAP dovecot reported:
IMAP(username): file index-mail.c: line 105
(index_mail_get_fixed_field): assertion failed:
(buffer_get_used_size(buf) == data_size)

As soon as I delete the dovecot.index.cache file within the users
mailbox this error goes away. Great, but that now I have some questions:

1) Does the dovecot.index.cache file store/cache server specific
settings? If not why did it cause this error on the new box with exactly
the same dovecot version and dovecot.conf?
2) What will happen if I delete the dovecot.index.cache file for all
users? Will POP3 users have to re-download all their mail or will
dovecot simply reference the dovecot.index file in the absence of the
cache file?

If I've missed something on the wiki explaining all this please point me
in the right direction. Any help would be greatly appreciated.

Gavin