can't find point when column has index

[andy w]

I have a very complex scenario but I managed to drill this down to a simple situation:

DROP TABLE IF EXISTS t1;
DROP TABLE IF EXISTS t2;
DROP TABLE IF EXISTS t3;
CREATE TABLE t1 (p POINT);
CREATE TABLE t2 (p POINT, INDEX(p));
CREATE TABLE t3 (p POINT, INDEX(p)) ENGINE=MyISAM;

INSERT INTO t1 VALUES (POINTFROMTEXT('POINT(1 2)'));
INSERT INTO t2 VALUES (POINTFROMTEXT('POINT(1 2)'));
INSERT INTO t3 VALUES (POINTFROMTEXT('POINT(1 2)'));

SELECT COUNT(*) FROM t1 WHERE p=POINTFROMTEXT('POINT(1 2)');

+----------+
| COUNT(*) |
+----------+
| 1 |
+----------+
1 row in set (0.00 sec)


SELECT COUNT(*) FROM t2 WHERE p=POINTFROMTEXT('POINT(1 2)');

+----------+
| COUNT(*) |
+----------+
| 0 |
+----------+
1 row in set (0.00 sec)

SELECT COUNT(*) FROM t3 WHERE p=POINTFROMTEXT('POINT(1 2)');

+----------+
| COUNT(*) |
+----------+
| 1 |
+----------+
1 row in set (0.00 sec)


That is, when using InnoDB tables, MySQL cannot find a point if an index is defined in that column (table t2). However, if an index is not defined (table t1) or the engine is MyISAM (table t3) then the point is found.
Is this a bug or is it documented somewhere?