ActiveSync not getting certain calendar entries

[Garry]

I have a problem with an OX installation where some users can not get certain calendar entries on their mobile phones. After several tests we seem to have narrowed it down to calendar entries that have been created a longer time ago, no matter for when ... e.g., one entry for March 6th this years was created somewhere around December or so. It is not synchronized to the mobile phone, even when editing/changing it.

Is there any behavior problem in this way known?

Installation is scheduled to be updated, but currently running on V6.22.11R7/7.6.2R51 ...