This isn’t a bug. There’s a difference between simply selecting a condensing group from the list (e.g. in order to examine the settings that you have already made for that group) and activating the condensing change for that group, which has to be done by activating the check box for that row.
Perhaps it isn’t apparent to you, but you can only have a single condensing change at a particular rhythmic position, so when you open this dialog, you need to be able to both look at and change the settings for multiple condensing groups.