I defeated it!
Put JAVA_OPTS="-Dlog4j.configuration=file:/var/webmet/vt/WEB-
INF/classes/log4j.properties" in catalina.sh script.

The log end is:

[FBStatementFetcher,DEBUG] FBResultSet next - FBStatementFetcher
[GDS_Impl,DEBUG] op_allocate_statement
[GDS_Impl,DEBUG] sent
[GDS_Impl,DEBUG] op_response
[GDS_Impl,DEBUG] op_response resp_object: 3
[GDS_Impl,DEBUG] op_response resp_blob_id: 0
[GDS_Impl,DEBUG] op_response resp_data size: 0
[GDS_Impl,DEBUG] readStatusVector arg:isc_arg_gds int: 0
[GDS_Impl,DEBUG] received
[FBManagedConnection,DEBUG] preparing sql: select count("id")
from "permread" where "id"=? and "userid"=?
[GDS_Impl,DEBUG] op_prepare_statement
[GDS_Impl,DEBUG] sent
[GDS_Impl,DEBUG] op_response
[GDS_Impl,DEBUG] op_response resp_object: 0
[GDS_Impl,DEBUG] op_response resp_blob_id: 0
[GDS_Impl,DEBUG] op_response resp_data size: 1024
[GDS_Impl,DEBUG] readStatusVector arg:isc_arg_gds int: 0
[GDS_Impl,DEBUG] received
[GDS_Impl,DEBUG] parseSqlInfo started
[GDS_Impl,DEBUG] parseSqlInfo: first 2 bytes are 1796 or: 4, 7
[GDS_Impl,DEBUG] xsqlda.sqln read as 1
[GDS_Impl,DEBUG] new xsqlvar 0
[GDS_Impl,DEBUG] isc_info_sql_type 496
[GDS_Impl,DEBUG] isc_info_sql_sub_type 0
[GDS_Impl,DEBUG] isc_info_sql_scale 0
[GDS_Impl,DEBUG] isc_info_sql_length 4
[GDS_Impl,DEBUG] isc_info_sql_field COUNT
[GDS_Impl,DEBUG] isc_info_sql_relation
[GDS_Impl,DEBUG] isc_info_sql_owner
[GDS_Impl,DEBUG] isc_info_sql_alias COUNT
[GDS_Impl,DEBUG] parseSqlInfo ended
[GDS_Impl,DEBUG] op_info_sql
[GDS_Impl,DEBUG] sent
[GDS_Impl,DEBUG] op_response
[GDS_Impl,DEBUG] op_response resp_object: 3
[GDS_Impl,DEBUG] op_response resp_blob_id: 0
[GDS_Impl,DEBUG] op_response resp_data size: 1024
[GDS_Impl,DEBUG] readStatusVector arg:isc_arg_gds int: 0
[GDS_Impl,DEBUG] received
[GDS_Impl,DEBUG] parseSqlInfo started
[GDS_Impl,DEBUG] parseSqlInfo: first 2 bytes are 1797 or: 5, 7
[GDS_Impl,DEBUG] xsqlda.sqln read as 2
[GDS_Impl,DEBUG] new xsqlvar 0
[GDS_Impl,DEBUG] isc_info_sql_type 581
[GDS_Impl,DEBUG] isc_info_sql_sub_type 0
[GDS_Impl,DEBUG] isc_info_sql_scale 0
[GDS_Impl,DEBUG] isc_info_sql_length 8
[GDS_Impl,DEBUG] isc_info_sql_field
[GDS_Impl,DEBUG] isc_info_sql_relation
[GDS_Impl,DEBUG] isc_info_sql_owner
[GDS_Impl,DEBUG] isc_info_sql_alias
[GDS_Impl,DEBUG] new xsqlvar 1
[GDS_Impl,DEBUG] isc_info_sql_type 581
[GDS_Impl,DEBUG] isc_info_sql_sub_type 0
[GDS_Impl,DEBUG] isc_info_sql_scale 0
[GDS_Impl,DEBUG] isc_info_sql_length 8
[GDS_Impl,DEBUG] isc_info_sql_field
[GDS_Impl,DEBUG] isc_info_sql_relation
[GDS_Impl,DEBUG] isc_info_sql_owner
[GDS_Impl,DEBUG] isc_info_sql_alias
[GDS_Impl,DEBUG] parseSqlInfo ended
[GDS_Impl,DEBUG] op_execute
[GDS_Impl,DEBUG] sent
[GDS_Impl,DEBUG] op_response
[GDS_Impl,DEBUG] op_response resp_object: 1
[GDS_Impl,DEBUG] op_response resp_blob_id: 0
[GDS_Impl,DEBUG] op_response resp_data size: 0
[GDS_Impl,DEBUG] readStatusVector arg:isc_arg_gds int: 0
[GDS_Impl,DEBUG] received
[GDS_Impl,DEBUG] op_fetch
[GDS_Impl,DEBUG] sent
[GDS_Impl,DEBUG] op_response
[GDS_Impl,DEBUG] op_response resp_object: 0
[GDS_Impl,DEBUG] op_response resp_blob_id: 0
[GDS_Impl,DEBUG] op_response resp_data size: 0
[GDS_Impl,DEBUG] readStatusVector arg:isc_arg_gds int: 335544344
[GDS_Impl,DEBUG] readStatusVector string: null
[GDS_Impl,DEBUG] readStatusVector string: null
[GDS_Impl,DEBUG] readStatusVector arg:isc_arg_gds int: 335544734
[GDS_Impl,DEBUG] readStatusVector string: null
[GDS_Impl,DEBUG] op_rollback
[GDS_Impl,DEBUG] sent
[GDS_Impl,DEBUG] op_response
[GDS_Impl,DEBUG] op_response resp_object: 0
[GDS_Impl,DEBUG] op_response resp_blob_id: 0
[GDS_Impl,DEBUG] op_response resp_data size: 0
[GDS_Impl,DEBUG] readStatusVector arg:isc_arg_gds int: 0
[GDS_Impl,DEBUG] received
[FBManagedConnectionFactory,DEBUG] About to detach db
[GDS_Impl,DEBUG] op_detach
[GDS_Impl,DEBUG] sent
[GDS_Impl,DEBUG] op_response
[GDS_Impl,DEBUG] op_response resp_object: 0
[GDS_Impl,DEBUG] op_response resp_blob_id: 0
[GDS_Impl,DEBUG] op_response resp_data size: 0
[GDS_Impl,DEBUG] readStatusVector arg:isc_arg_gds int: 0
[GDS_Impl,DEBUG] received
[GDS_Impl,DEBUG] About to invalidate db handle
[GDS_Impl,DEBUG] successfully invalidated db handle

I swear it desided to 'op_rollback' - 'op_detach' by itself... But
why? No 'fatals' there.