This is due to Bug 6156624 which is fixed in 12c.  The "bug" is that binds are not converted into a string for the value_string column. Here is an example test case:

SQL> declare

bindts timestamp;

begin

bindts := systimestamp();

execute immediate 'select /* BIND_CAPTURE_TEST */ 1 from dual where :b1 is

not null' using bindts;

execute immediate 'select /* BIND_CAPTURE_TEST */ 1 from dual where :b1 is

not null' using bindts;

execute immediate 'select /* BIND_CAPTURE_TEST */ 1 from dual where :b1 is

not null' using bindts;

end;

/

PL/SQL procedure successfully completed.

SQL> select sql_id from v$sql where sql_fulltext like '%BIND_CAPTURE_TEST%'

and sql_fulltext not like '%xxx%' and command_type = 3;

SQL_ID 
------------- 
1mf1ch9vsr06a

SQL> SELECT

   a.sql_text,

   b.name,

   b.POSITION,

   b.datatype_string,

   b.value_string

FROM

  v$sql_bind_capture b,

  v$sqlarea          a

WHERE

   b.sql_id = '3t7wc8aftsr0z'

AND

   b.sql_id = a.sql_id;

So here the value_string for timestamp is showing null which is actually not. It can be obtained using a workaround of selecting the bind data via "ANYDATA.AccessTimestamp(value_anydata)".

SQL> SELECT

   a.sql_text,

   b.name,

   b.POSITION,

   b.datatype_string,

   b.value_string,

   ANYDATA.AccessTimestamp(value_anydata)

FROM

  v$sql_bind_capture b,

  v$sqlarea          a

WHERE

   b.sql_id = '3t7wc8aftsr0z '

AND

   b.sql_id = a.sql_id;

For more information please check Doc ID 444551.1