Microseconds not compared in TIMESTAMP(6)

[Andrew Hutchings]

drizzle> select * from t1;
+------+----------------------------+
| a | b |
+------+----------------------------+
| 1 | 2011-04-14 00:18:42.539939 |
| 2 | 2011-04-14 00:18:42.539910 |
+------+----------------------------+
2 rows in set (0.000438 sec)

drizzle> select * from t1 join t1 as t2 on (t1.b=t2.b);
+------+----------------------------+------+----------------------------+
| a | b | a | b |
+------+----------------------------+------+----------------------------+
| 1 | 2011-04-14 00:18:42.539939 | 1 | 2011-04-14 00:18:42.539939 |
| 2 | 2011-04-14 00:18:42.539910 | 1 | 2011-04-14 00:18:42.539939 |
| 1 | 2011-04-14 00:18:42.539939 | 2 | 2011-04-14 00:18:42.539910 |
| 2 | 2011-04-14 00:18:42.539910 | 2 | 2011-04-14 00:18:42.539910 |
+------+----------------------------+------+----------------------------+
4 rows in set (0.000556 sec)