iPhone not syncing trash/deleted mail.

Hi,

My iMac will sync trashed mail to MobileMe and vice versa.

My iPhone will recieve above trashed mail, but if trashed on handset-will not sync back to iMac or MobileMe.

My iPad will however sync it's trashed mail to iMac/MobileMe and back from them, but not to iPhone.

Any tips on why iPhone won't?

On Lion, latest firmware for IOS devices.

Thanks.