New event disappear on iPhone calendar

The summary of this question is below.

[Environment]

- iPhone IOS 7.0.4,

- MS Exchange 2008 (using ActiveSync to see outlook mail by iPhone).

[Problem]

1. Creating new event on Outlook, the event is reflected iPhone calendar correctly.
2. Creating new event on iPhone calendar, the event is reflected to Outlook, but the event disappear on iPhone calendar.

In the case of 1, it is correct action.

But in the case of 2, it is very strange action.

Does someone experience similar problem?

If you have any solution of this, please let me know.

Kind and Regards,