Wrong binlog entry for BLOB on a blackhole intermediary master

Originally reported at https://bugs.mysql.com/bug.php?id=93917
 
Description:
 
Bug #56007
seems to be silently fixed. However, the same issue exists for a BLOB column.
How to repeat:
Run the attached test case, then check binary logs on the slave.

Test column changes recorded correctly.

Original update:

UPDATE BLACK SET TEXTCOL='teststring_update' where ID=1;

Binlog entry:

1. 1. 1. UPDATE `test`.`BLACK`
      2. WHERE
      3. @1=1 /* LONGINT meta=0 nullable=1 is_null=0 */
      4. @2='teststring' /* BLOB/TEXT meta=2 nullable=1 is_null=0 */
      5. @3='TESTBLOB' /* BLOB/TEXT meta=2 nullable=1 is_null=0 */
      6. SET
      7. @1=1 /* LONGINT meta=0 nullable=1 is_null=0 */
      8. @2='teststring_update' /* BLOB/TEXT meta=2 nullable=1 is_null=0 */
      9. @3='TESTBLOB' /* BLOB/TEXT meta=2 nullable=1 is_null=0 */

Update for a BLOB column not.

Original update:

UPDATE BLACK SET BLOBCOL='testblob_update' where ID=2;

Binlog entry:

1. 1. 1. UPDATE `test`.`BLACK`
      2. WHERE
      3. @1=2 /* LONGINT meta=0 nullable=1 is_null=0 */
      4. @2='TESTSTRING_2' /* BLOB/TEXT meta=2 nullable=1 is_null=0 */
      5. @3='testblob_u' /* BLOB/TEXT meta=2 nullable=1 is_null=0 */
      6. SET
      7. @1=2 /* LONGINT meta=0 nullable=1 is_null=0 */
      8. @2='TESTSTRING_2' /* BLOB/TEXT meta=2 nullable=1 is_null=0 */
      9. @3='testblob_update' /* BLOB/TEXT meta=2 nullable=1 is_null=0 */