What do you mean by 'syncing'? do they open it as a shared folder or a shared mailbox? is th custom field on a custom form or is it a field in the folder?
By 'syncing' I mean reflecting updates in other user folder.
It is custom field on folder and not custom form. we have defined custom fields ( with same name ) on task folder with all users. When user A assigns and send task to user B, user B updates. Only text field updates are reflected in user A folder. Date field updates do not reflect in user A folder.