Not always overfilling. German wines just leak. Despite perfect provenance (including bottles hand carried home from Germany) cork-finished German wines sometimes leak, especially going up the pradikat scale.
Same here. We live in a part of the country that can get ridiculously hot. Had one winery deliver to us guaranteed climate controlled but that was only to Albuquerque. From there to here, climate controlled was the windows rolled down. The wine was still OK but a funny sight to see.