Database tracing interrupts with error message "Unknown tag (0) in isc_svc_query() results ", after random amounts of time, at different points.

Used commandline:
/opt/firebird/bin/fbsvcmgr localhost:service_mgr user SYSDBA password action_trace_start trc_cfg /opt/firebird/fbtrace.conf.tester_db

Trace configuration file:
<database>
        enabled false
        max_log_size 0
        log_connections true
        log_transactions true
        log_statement_prepare false
        log_statement_free true
        log_statement_start true
        log_statement_finish true
        log_procedure_start true
        log_procedure_finish true
        log_trigger_start true
        log_trigger_finish true
        print_plan true
        print_perf false
        log_blr_requests false
        print_blr false
        log_dyn_requests false
        print_dyn false
        time_threshold 100
        max_sql_length 3000
        max_blr_length 500
        max_dyn_length 500
        max_arg_length 80
        max_arg_count 30
</database>
<services>
        enabled false
        max_log_size 0
        log_services false
        log_service_query false
</services>
<database %[\\/]ptdb.fdb>
        enabled true
</database>