syncing ical iPod Touch 2nd with iPad and iMac

Without any problem I can

- sync iCal on my iPod Touch 2nd generation (OS 4.2.1) with my iMac using iTunes. All events entered on my iPod Touch appear in iCal and vice versa.

- sync iCal on my iPad with my iMac using iCloud. All events entered on my iPad appear in iCal and vice versa.

- sync events entered on my iPad with iCal on my iPod Touch

However, I cannot sync any of the events that I entered on my iPod Touch with my iPad, although these events can be seen in iCal on my iMac.

What is causing this and how can I solve this problem. One thing though: I prefer syncing my iPad using iCloud...