Bug #1547 "SELECT ... WHERE field = var" sometimes give the wrong result in SPs

Description:
In some cases queries "SELECT ... INTO ... WHERE field = var" fails to match the
correct row when executed in a stored procedure (where "var" is a local
variable).
It seems this is because the WHERE clause returns true when it shouldn't.
However, in other test cases similar selects works, so it's somewhat
intermittent.

How to repeat:
Run this:
---
delimiter |;
create procedure frob(s char(16))
begin
  declare x int;

  select data into x from t1 where id = s limit 1;
  if x > 10 then
    insert into t1 values ("less", x-10);
  else
    insert into t1 values ("more", x+10);
  end if;
end|

insert into t1 values ("foo", 12), ("bar", 7)|
call frob("foo")|
call frob("bar")|
select * from t1|
---

The result is:
+------+------+
| id   | data |
+------+------+
| foo  |   12 |
| bar  |    7 |
| less |    2 |
| less |    2 |
+------+------+

but there should be only one "less" row, and one row with "more 17".
Apparently, the select always picks the first (foo) row, despite the
where condition.

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