It's probably just a variance in the ceramic. Making anything identical out of ceramics is a challenge. Ceramics start out wet, then get fired and cured. Getting absolute precision from anything ceramic can be challenging. I suspect yours is a tick out of tolerance.
I just use the stainless steel bowl on mine. I saw too many of the glass bowls break on cooking shows to want to get one of those. (I think two broke on one episode of the Great British Bakeoff and I saw another one break on another cooking show. (Maybe on one of the Bon Appetit web series?) Stainless steel just won't break.
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