You cant see them well until the edge guide rods are removed, but there is a centering vee for the rods cast into the base which create stress risers under the thumb screw. Look close and you can just make out the top of the vee.
Yer right, its a poor design. I'll be getting over to Bosch Monday.
Ya kno Tim, I havent even taken the base plate off (had to finish the fluting op and didnt see it as a hinderance to the final round over op) but you could be right. Maybe a casting core is positioned to close to the area under the guide rod saddle.
Think Im gonna leave it as is for our visit to Bosch.