Recent kdepim* 4.14 has a regression in which remote changes to message read and/or "important" (starred) states are not always synced reliably. I generally run into this issue coming back to kmail on Mac OS X after having used kmail 4.13.3 on a Linux host, but when it strikes, one can login to gmail's web interface, and toggle the read state of a whole thread without that this change is reflected in the running kmail instance.

akonadi 1.13.1 commit 9c0dc6b
kdepimlibs v4.14.10-16-g2e7d344
kdepim v4.14.10-7-g48cfa63
kdepim-runtime v4.14.10 commit b3bfa11

this issue does NOT occur when using KDE PIM (libs and runtime included) 4.13.3 (release) with the same akonadi version.

Reproducible: Sometimes

Steps to Reproduce:
1. install the kdepimlibs, kdepim-runtime and kdepim versions cited in the summary
2. define an imap account hosted on GMail and open one of its folders in kmail2
3. induce a read state change outside of kmail, for instance through gmail's web interface
4. induce an "important" state change the same way (click the star)

Actual Results:  
Sometimes the state is synced correctly, sometimes it isn't. I have not yet found a way to make it sync when it doesn't (restarting kmail and all agents does NOT help), and haven't yet had the patience to wait to see if it settles itself in time.
kmail DOES SHOW a progress indicator suggesting that a sync takes place as soon as I activate the window after effectuating a change via gmail.com , so IMAP IDLE apparently works to some extent.

Expected Results:  
Messages are shown as (un)read and/or (un)important as a function of settings made outside of the running kmail instance, be it via kmail on another host or via the gmail.com website. This information is updated as soon as it becomes available, through IMAP IDLE or a scheduled or manual sync.

Reverting to kde pim release 4.13.3 restores proper behaviour without a change in the akonadi version.
Inquiry on the kdepim-users ML showed that at least 1 other user is concerned, apparently on OpenSuse.