the test was doing

--replace_result $con_id con_id
eval SHOW EXPLAIN FOR $con_id;

with the intention of replacing the variable part of the statement
in the result log. But actually replace_result replaces everything
that matches. In particular, when $con_id is 100, the warning

Note   1003    select sleep(100000)

becomes

Note   con_id3    select sleep(con_id000)