I don't know about the experience of others, but I have found that brass bushings seem to be a tighter fit than bronze ones of the same size. I have thought that perhaps the softer brass ones tend to "gall" a bit when driven in, helping them to stay tighter. The bronze ones are much harder, and tend not to gall.
I too run into the odd bushing that is too loose once the hole is reamed with an appropriate reamer. Fortunately, it is not a regular occurrence. Could it be that perhaps you had tried to insert a bushing that went in crooked, stretching the hole a bit on the way in? I use a hole closing punch to solve this kind of problem.