Trouble adding a parked domain

Hi, I'm trying to add a parked domain so that it goes to the same spot as the normal domain. When I added it in cpanel, I chose the same directory (public_html).

Right now, parkeddomain.com works, but if I go to www.parkeddomain.com, I have to add /index.htm for it to load (otherwise it loads defaultwebpage.cgi).

And this is strange too, I created a sub domain for the parked domain, and www.subdomain.parkeddomain.com works! If I visit subdomain.parkeddomain.com, it loads defaultwebpage.cgi.

I tried adding A records but sometimes it would say successful then they wouldn't show up in the user-added list at the bottom.

I'm rather new to this, but I do have a little experience. When I registered parkeddomain.com, I used the same nameservers as normaldomain.com