unable to get join of two tables to use the spatial index provided

[Galt Barber]

I can't get the spatial index to be used in a simple join!

mysql> desc allEstGeo;
+-------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| qName | varchar(255) | NO | | | |
| tName | varchar(255) | NO | | | |
| span | geometry | NO | MUL | | |
+-------+--------------+------+-----+---------+-------+
has 1.3 million rows

mysql> desc xrfGeo;
+-------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| name | varchar(255) | NO | | | |
| chrom | varchar(255) | NO | | | |
| span | geometry | NO | MUL | | |
+-------+--------------+------+-----+---------+-------+
has 194 thousand rows

Both of these have a spatial index on span.

mysql> explain select qName, name from xrfGeo x, allEstGeo e where Intersects(x.span, e.span);
+----+-------------+-------+------+---------------+------+---------+------+---------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+------+---------+-------------+
| 1 | SIMPLE | x | ALL | span | NULL | NULL | NULL | 194546 | |
| 1 | SIMPLE | e | ALL | span | NULL | NULL | NULL | 1343137 | Using where |
+----+-------------+-------+------+---------------+------+---------+------+---------+-------------+

Even using use index(span) or force index(span) in the
from clause does not help.
What is the point of having a spatial index if it can't be used?

Note: in the case of looking up one value it does work:

mysql> explain select qName, tName, asText(span) from allEstGeo where intersects(span,GeomFromText('LINESTRING(26729 102834029,39573 102834029)'));
+----+-------------+-----------+-------+---------------+------+---------+------+------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-----------+-------+---------------+------+---------+------+------+-------------+
| 1 | SIMPLE | allEstGeo | range | span | span | 32 | NULL | 1 | Using where |
+----+-------------+-----------+-------+---------------+------+---------+------+------+-------------+


In case you are curious, each span basically contains two points
defining the ends of a segment on a chromosome. Each table
is a different data track. I am interested in using mysql to
create the intersection between the tracks. i.e. what particular genes
does each EST tag intersect with?

I assume this is SUPPOSED to work.

-Galt