Bulk Delete of Users Fails on MS SQL Server

MS SQL 2008 v10/IIS7.5/Windows Server 2008R2

Site Admin -> Users -> Accounts -> Bulk User Administration

Select one user to delete - OK
Select two or more users to delete - error below

I did report a similar error with 2.2 ages ago - has it reoccurred again? Sorry I don't know the number.

Developer Debug below

Debug info: SQLState: 42000<br>
Error Code: 3988<br>
Message: [Microsoft][SQL Server Native Client 11.0][SQL Server]New transaction is not allowed because there are other threads running in the session.<br>

native sqlsrv_begin_transaction
[NULL]
Error code: dmlreadexception
Stack trace:
line 407 of \lib\dml\moodle_database.php: dml_read_exception thrown
line 258 of \lib\dml\sqlsrv_native_moodle_database.php: call to moodle_database->query_end()
line 1368 of \lib\dml\sqlsrv_native_moodle_database.php: call to sqlsrv_native_moodle_database->query_end()
line 2101 of \lib\dml\moodle_database.php: call to sqlsrv_native_moodle_database->begin_transaction()
line 928 of \lib\completionlib.php: call to moodle_database->start_delegated_transaction()
line 524 of \lib\completionlib.php: call to completion_info->internal_set_data()
line 1157 of \lib\completionlib.php: call to completion_info->update_state()
line 836 of \lib\grade\grade_grade.php: call to completion_info->inform_grade_changed()
line 284 of \lib\grade\grade_object.php: call to grade_grade->notify_changed()
line 1306 of \lib\gradelib.php: call to grade_object->delete()
line 3898 of \lib\moodlelib.php: call to grade_user_delete()
line 30 of \admin\user\user_bulk_delete.php: call to delete_user()