Version:            (using KDE KDE 3.5.0)
Installed from:    Fedora RPMs
OS:                Linux

Kmail's offline IMAP mode has a reproducible bug:

1. Setup an offline IMAP account with some folders, and configure it
to only synchronise with a manual check, so we can control when the
sync occurs
2. Assume you have a folder A with N messages and folder B with M messages.
3. Move 1 message from A to B. The folder message counts are now:

A: N-1
B: M+1

4. Perform a sync by pressing CTRL-L
5. Now observe the folder message counts. They will be as follows:

A: N-1
B: M

6. Therefore, B's folder count has gone back to the value it was before the sync.
7. Now, without making any changes, perform another sync with CTRL-L
8. This time, the folder message counts will be correct

It appears that if a folder's contents change during a sync, the folder count isn't updated correctly. Specifically, it seems to happen in the case when messages are added to a folder.

I'm using Kmail against courier-imap version 4.0.6, but I don't think this has anything to do with the IMAP server used.