No backgoundfor closed captions

I am going to ask the 2nd silliest question today.

I am running the latest editon of primere pro and have the closed captions in properly or at least I think so. When I que the file into media encoder the closed captions background is transparent. This is despite the fact that a black opaque background was selected in the captions tab. I am using standard CEA-708 stream cc1 and 25fps. I am adding  as a sidecar.