Don't know if this is the same thing you are speaking of without a picture, however I had an issue with the last round of my magazine getting stuck, very similiar to your description but, I don't know if this is happening only on your last round. The fix for me required nothing more than a file and about 5 minutes time.
I also have seen a friends stock Kimber mags not feed the last round because of a slight bump in the magazine shelf catching the lip of the casing. EVERYTIME, a little grinding with a dremel and that was fixed.