In the rule that blocks removable devices, check the box that says "Exclude" for the definition created for CD/DVD.
That was a no go. I was still able to write to cds. I even tried blocking the cd/dvdrw and that did not work either. It seems that it only works when I check the cd/dvd within my active usb block rule. Any other combos that you can think.
You have two rules, right?
Create the rule for where you block all removable media except the definition for cd/dvd
Create a removable media rule for cd/dvd that makes them read-only
Make sure both of them apply to the same user assignment group.