After OS upgrade 10.7.3 - 10.7.5 imap messages in mail keep loading

Question

Hi,
i updated osx yesterday from 10.7.3 to 10.7.5 and now apple mail is acting up.
I have several accounts in mail. Two are imap accounts of my own domains. Others are imap googlemail accounts.
Since the upgrade, i cannot view messages older than a certain age anymore from the selfhosted accounts.
On the webserver, the messages are deleted a month after they have been donwloaded to apple mail.
If i select a message older than "today" as in ones that have freshly been retrieved from the server today, the loader keeps spinning and "Loading..." appears endlessly.
Shouldn't these messages still all be on my local computer? No matter if there is something on the server or not?
I have made no changes to the account settings in mail.
I have set up one of the accounts as a new (duplicate) to see what happens. It downloaded those messages, that were less old than a month and therefore still on the server. I can view them.
In the corresponding old account, i can't even view a message from yesterday.
I am at wits end and loosing all my "old" correspondation would be an absolute disaster.
cheers upfront for any hints!
flo

Answer 1

ps:
dug deeper and have had a look in the /users/.../Library/Mail/V2 Folder (thanks osx for hiding "Library" again ) and found the two Folders of these two accounts in Question.
It seems true - all Messages have been wiped of my drive. The only messages in there are the ones, retrieved this morning.
There is no apparent reason to me, why a System update would want to touch downloaded messages at all. I consider this quite a bug.