UPDATE: There's no issue changing reminders using the reminders app on icloud.
For now my workaround will just be to use the icloud site on my computer for the reminder list.
It seems like the only time I have an issue is when I try to update the reminders in ical on my computer.
I checked to see if the app store had a reminders only app - similar to what's on my iphone and the icloud site - but I couldn't find one.
Maybe the issue has to do with the fact that the iphone and icloud have a reminders list separate from the calendar - but it seems odd that the reminders in ical doesn't seem to have the same funcionality.