WiFi sync of iPhone Calendar with Hotmail

I have used my iPhone to access my hotmail emails without any problems for about a year .

I have now added the required settings to Microsoft Exchange on my iPhone for it's calendar to sync over the air with my hotmail calendar. However it only seems to work one way.

• Hotmail appointments get transferred to the iPhone calendar, however all iPhone appointments then disappear.
• Any appointments subsequently added on the iPhone are not transferred to the Hotmail calendar.

Any ideas please?