Only another shub user on the same package on your UBR can give you a definitive answer
Other than that the only way I see is to get it activated and see for yourself.
I mention modem mode because reports indicate it is solid. As far as I know, I have seen no reports of the issue you describe by anyone using modem mode. Indeed I have not seen any reports on the issue you describe for quite some time but that is not to say it has been rectified.