iPhone Calendar and iCal

At the moment on my iPhone, the calendars I have are "All From My Mac"
and "All Mobile Account". They both contain essentially the same
information and therefore if I select "Show all Calendars", I get two of
each event. How is it possible to not have the "All From My Mac"
calendars appear on the iPhone?

I tried in iTunes by de-selecting "Sync iCal Calendars" under the Info
tab but it made no difference. I also noticed that when I do that, the
"Replace Information on this iPhone > Calendars" is ghosted out and
cannot be selected.

Also, if I deselect all the calendars under the Info tab and then select
Sync iCal Calendars > Selected Calendars, it automatically reverts to
syncing "All calendars" the next time I sync.

Any help would be greatly appreciated.

TIA,
ausdan