Bug #10390 SELECT MAX(a_datetime_field) returns a String rather than a Timestamp

Description:
A JDBC query with a GROUP BY clause that SELECTs MAX or MIN on a MySQL datetime field returns a String rather than the expected Timestamp.  A JDBC query with NO GROUP BY clause that SELECTs MAX or MIN on a MySQL datetime field returns the expected Timestamp.  

How to repeat:
Using Java 1.4.2 and mysql-connector-java-3.1.8a or 3.0.15, Query a MySql table "sometable" containing a datetime "datetime1" field and some other field "otherfield" to which a group by clause can be applied, to return a result set.

Perform the following Java JDBC query:
String sql = "SELECT datetime1 FROM sometable";
ResultSet rs = mystatement.executeQuery(sql);

Check the object type of the column returned for the datetime field:
rs.next();
String class = rs.getObject("datetime1").getClass().getName();
class = "Timestamp" as expected

Now add a MAX aggregate to the query
sql = "SELECT MAX(datetime1) FROM sometable";
rs = mystatement.executeQuery(sql);
rs.next();
class = rs.getObject("datetime1").getClass().getName();
class = "Timestamp" as expected

Now add a GROUP BY clause to the query
sql = "SELECT MAX(datetime1) FROM sometable GROUP BY otherfield";
rs = mystatement.executeQuery(sql);
rs.next();
class = rs.getObject("datetime1").getClass().getName();
class = "String", NOT "Timestamp"

Suggested fix:
The statement with the group by clause should return a Timestamp, NOT a String

I tried to repeat the bug but got right results for each request:

Class: java.sql.Timestamp
Class: java.sql.Timestamp
Class: java.sql.Timestamp

Maybe I created the table with other definition. Could you please  write here definition of your table.
I attached my test case to "Files".

Test case

Attachment: test.java (text/plain), 1.37 KiB.

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