I have two users with Android devices (using ActiveSync) for which a two-way sync with Zimbra is not occurring.
For example, if a user reads her message on the phone it still shows as unread on the web client. HOWEVER, if she reads it on the ZWC FIRST, then it shows as read on the Android device.
This particular user has Android version 2.3.4 on her device. Her coworker has version 2.3.3.
On the server side, it's Release 7.1.3_GA_3346.RHEL5_64_20110928134534