Originally this bug was reported by Philip Stoev in the bug entry #603654. after the fix for bug #603654 had been committed. Though the bug triggers the same assertion failure it differs from the bug originally reported in the bug entry ##603654 .
The new bug can be reproduced with following simple test case:
CREATE TABLE t1 (
a char(255), b char(255), c char(255), d char(255),
v char(255) AS (CONCAT(c,d) ) VIRTUAL
);
INSERT INTO t1(a,b,c,d) VALUES ('w','x','y','z'), ('W','X','Y','Z');
SELECT v FROM t1 ORDER BY CONCAT(a,b);