Scenario:

SQL> create database 't1.fdb'; commit;
SQL> create table t(s blob); commit;
SQL> quit;

Window #1
#########
// Connect to database via TCP
C:\MIX\firebird\fb25>isql localhost:C:\MIX\firebird\fb25\T1.FDB -n
Database: localhost:C:\MIX\firebird\fb25\T1.FDB

Window #2
#########
Starting user trace session with enabled parameters:
  log_connections true
  log_transactions true
  log_statement_start true
  log_statement_finish true

Window #1
#########
insert into table `t` large blob and press Ctrl-Break (*not* Ctrl-C!).

SQL> insert into t select list(f1.rdb$field_name) from rdb$fields f1,rdb$fields,rdb$fields;

The result of this action depends on when I press Ctrl-Break:
variant-1: press Ctrl-Break at the time when ISQL performs statement, i.e. do NOT wait finish of it;
variant-2: press Ctrl-Break after ISQL has finished statement and returns to prompt.

Trace for variant-1:
###############

insert into t select list(f1.rdb$field_name) from rdb$fields f1,rdb$fields,rdb$fields

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
PLAN JOIN (F1 NATURAL, RDB$FIELDS NATURAL, RDB$FIELDS NATURAL)

0 records fetched

   5723 ms, 1 read(s), 8120 write(s), 2165331 fetch(es), 26376 mark(s)



Table Natural Index Update Insert Delete Backout Purge Expunge

***************************************************************************************************************

RDB$FIELDS 1039419



2013-03-25T13:00:15.2960 (588:0220DEB0) ERROR AT jrd8_execute

C:\MIX\FIREBIRD\FB25\T1.FDB (ATT_3, SYSDBA:NONE, NONE, TCPv4:127.0.0.1)

C:\MIX\firebird\fb25\bin\isql.exe:2404

335544794 : operation was cancelled


2013-03-25T13:00:15.3120 (588:0220DEB0) ROLLBACK_TRANSACTION

C:\MIX\FIREBIRD\FB25\T1.FDB (ATT_3, SYSDBA:NONE, NONE, TCPv4:127.0.0.1)

C:\MIX\firebird\fb25\bin\isql.exe:2404

(TRA_8, CONCURRENCY | WAIT | READ_WRITE)

     13 ms, 8 read(s), 34 write(s), 9141 fetch(es), 9132 mark(s)

Trace for variant-2 (when ISQL has finished statement):
###############
insert into t select list(f1.rdb$field_name) from rdb$fields f1,rdb$fields,rdb$fields

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
PLAN JOIN (F1 NATURAL, RDB$FIELDS NATURAL, RDB$FIELDS NATURAL)

0 records fetched

   8156 ms, 3 read(s), 14695 write(s), 3722041 fetch(es), 46065 mark(s)



Table Natural Index Update Insert Delete Backout Purge Expunge

***************************************************************************************************************

RDB$FIELDS 1786323

T 1



2013-03-25T13:00:49.1710 (588:0220DEB0) COMMIT_TRANSACTION -- <<<<<<<<<<<<<< ??? W H Y ??? <<<<<<<<<<

C:\MIX\FIREBIRD\FB25\T1.FDB (ATT_4, SYSDBA:NONE, NONE, TCPv4:127.0.0.1)

C:\MIX\firebird\fb25\bin\isql.exe:1740

(TRA_9, CONCURRENCY | WAIT | READ_WRITE)

    120 ms, 1 read(s), 1019 write(s), 1 fetch(es), 1 mark(s)

PS.
SQL> show version;
ISQL Version: WI-V2.5.3.26556 Firebird 2.5
Server version:
Firebird/x86/Windows NT (access method), version "WI-V2.5.3.26556 Firebird 2.5"
Firebird/x86/Windows NT (remote server), version "WI-V2.5.3.26556 Firebird 2.5/tcp (csprog)/P12"
Firebird/x86/Windows NT (remote interface), version "WI-V2.5.3.26556 Firebird 2.5/tcp (csprog)/P12"
on disk structure version 11.2