Submitted by: @pavel-zotov

Test:
#⁠#⁠#⁠#⁠

shell del C:\MIX\firebird\QA\fbt-repo\tmp\test.fdb 2>nul;
set names utf8;
create database '/:C:\MIX\firebird\QA\fbt-repo\tmp\test.fdb' default character set utf8;

recreate table t1 (
n0 int
,blob_fld_w1252
blob
character set win1252
,c_implicit_type_of_blob_field
computed by ( blob_fld_w1252 )
,c_explicit_blob_on_blob_field
blob ------------------------------------------------------------------------------------------------------ [ 1 ]
computed by ( blob_fld_w1252 )
,c_transitive_on_implicit_type
computed by ( c_implicit_type_of_blob_field )
,c_transitive_on_explicit_blob ----------------------------------------------------------------------- [ 2 ]
computed by ( c_explicit_blob_on_blob_field )
);

insert into t1 values(null,'ä');
commit;

set sqlda_display on;
set blob all;
set list on;
select * from t1;

Run:
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isql -q -i test.sql 1>test.log & isql -x /:C:\MIX\firebird\QA\fbt-repo\tmp\test.fdb >meta.log

Content of 'test.log':
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INPUT message field count: 0

OUTPUT message field count: 6
01: sqltype: 496 LONG Nullable scale: 0 subtype: 0 len: 4
: name: N0 alias: N0
: table: T1 owner: SYSDBA
02: sqltype: 520 BLOB Nullable scale: 0 subtype: 1 len: 8 charset: 4 UTF8
: name: BLOB_FLD_W1252 alias: BLOB_FLD_W1252
: table: T1 owner: SYSDBA
03: sqltype: 520 BLOB Nullable scale: 0 subtype: 1 len: 8 charset: 4 UTF8
: name: C_IMPLICIT_TYPE_OF_BLOB_FIELD alias: C_IMPLICIT_TYPE_OF_BLOB_FIELD
: table: T1 owner: SYSDBA
04: sqltype: 520 BLOB Nullable scale: 0 subtype: 0 len: 8 ------------------------------------------------------------------------------------------------------ [ A ]
: name: C_EXPLICIT_BLOB_ON_BLOB_FIELD alias: C_EXPLICIT_BLOB_ON_BLOB_FIELD
: table: T1 owner: SYSDBA
05: sqltype: 520 BLOB Nullable scale: 0 subtype: 1 len: 8 charset: 4 UTF8
: name: C_TRANSITIVE_ON_IMPLICIT_TYPE alias: C_TRANSITIVE_ON_IMPLICIT_TYPE
: table: T1 owner: SYSDBA
06: sqltype: 520 BLOB Nullable scale: 0 subtype: 0 len: 8 ------------------------------------------------------------------------------------------------------ [ B ]
: name: C_TRANSITIVE_ON_EXPLICIT_BLOB alias: C_TRANSITIVE_ON_EXPLICIT_BLOB
: table: T1 owner: SYSDBA

N0 <null>
BLOB_FLD_W1252 0:9
ä
C_IMPLICIT_TYPE_OF_BLOB_FIELD 0:6
ä
C_EXPLICIT_BLOB_ON_BLOB_FIELD 80:0
ä
C_TRANSITIVE_ON_IMPLICIT_TYPE 0:3
ä
C_TRANSITIVE_ON_EXPLICIT_BLOB 80:0
ä

Lines marked in DDL by [1] and [2] corresponds to [A] and [B] in the output.
When definition of COMPUTED-BY field contains explicit specification of its type (keyword "BLOB") then such field charset and sub_type disappears from SQLDA_DISPLAY output. The same will be when computed-by field is based on computed-by which, in turn, is declared with explicit "BLOB" keyword in its own DDL.

Checked on: WI-V3.0.0.32306.