A group_concat call with a subselected SUM (or AVG) in the order by phrase wil fail with
"ERROR 1815 (HY000): Internal error: IDB-2035: An internal error occurred. Check the error log file & contact support."
debug.log will contain "/home/calpont/mariadb/engine/utils/rowgroup/rowgroup.h@726: assertion '0' failed"
The problem is that the order by portion of group_concat is not long double aware.