Why is exception not thrown in AseCommand when "Truncation error occurred"?

Question

In the below SQL, data is written to SOURCE and from there to TARGET.
The DECIMAL columns in TARGET are deliberately smaller than those in SOURCE (eg a DECIMAL (12, 2) column populated from a DECIMAL (19,11) source).
When I run this in an Query tool (eg, SqlDbx) I get the messages:
"Truncation error occurred
Command has been aborted"
But when I run this using the .net Client (supplied with the Developer Edition of ASE 16.0) no exception is thrown (the INSERT fails though).  The method is AseCommand.ExecuteNonQuery().
Is this deliberate? 
Is this believed to be correct?
How can I tell that a truncation error has been raised?
Thanks
IF OBJECT_ID ('dbo.TARGET') IS NOT NULL
  DROP TABLE dbo.TARGET
GO
CREATE TABLE dbo.TARGET
  S_Name_NVARCHAR NVARCHAR (50) null,
    S_RedComponent_DEC_15_6 decimal(15, 6) NULL,
    S_BlueComponent_DEC_12_2 decimal(12, 2) NULL, 
    S_GreenComponent_DEC_18_10 decimal(18, 10) NULL
GO
IF OBJECT_ID ('dbo.SOURCE') IS NOT NULL
  DROP TABLE dbo.SOURCE
GO
CREATE TABLE dbo.SOURCE
  Name_NVARCHAR      NVARCHAR (2000) NULL,
  RedComponent_DEC   DECIMAL (19,11) NULL,
  GreenComponent_DEC DECIMAL (19,11) NULL,
  BlueComponent_DEC  DECIMAL (19,11) NULL
GO
INSERT INTO dbo.SOURCE (Name_NVARCHAR, RedComponent_DEC, GreenComponent_DEC, BlueComponent_DEC)
VALUES ('Beige', 272.195, 272.195, 244.42)
GO
INSERT INTO dbo.SOURCE (Name_NVARCHAR, RedComponent_DEC, GreenComponent_DEC, BlueComponent_DEC)
VALUES ('Bisque', 283.305, 253.308, 217.756)
GO
INSERT INTO dbo.SOURCE (Name_NVARCHAR, RedComponent_DEC, GreenComponent_DEC, BlueComponent_DEC)
VALUES ('Black', 0, 0, 0)
GO
INSERT INTO dbo.SOURCE (Name_NVARCHAR, RedComponent_DEC, GreenComponent_DEC, BlueComponent_DEC)
VALUES ('BlanchedAlmond', 283.305, 261.085, 227.755)
GO
--Is there data to migrate?
SELECT LEFT( S.Name_NVARCHAR,8000),S.GreenComponent_DEC,S.GreenComponent_DEC,S.GreenComponent_DEC
FROM (
SELECT * FROM SOURCE
) S
--Yes.migrate away!
--Next line gives a truncation error occurred in Sybase (gives a truncation error occurred in a query tool
--but fails silently in AseCommand.ExecuteNonQuery).
INSERT dbo.TARGET (S_Name_NVARCHAR,S_RedComponent_DEC_15_6,S_BlueComponent_DEC_12_2,S_GreenComponent_DEC_18_10)
SELECT LEFT( S.Name_NVARCHAR,8000),S.GreenComponent_DEC,S.GreenComponent_DEC,S.GreenComponent_DEC
FROM (
SELECT * FROM SOURCE
) S
select * from dbo.TARGET

Answer 1

Hi Dave,
I am consulting internally on this. To my understanding, this behavior is based on the ASE severity level, as returned in the TDS_EED token. AseExceptions are thrown when severity level is 11 or higher.
Our docs are not explanatory in this regard.  Once I get clarification we will provide something in the form of wiki or KBA or doc bug to further explain the detail.  Apologize for the delay and problems this caused. I guess since the command is aborted by ASE, therefore no insertion occurs, even though ASE indicates truncation occurs prior - makes this confusing.
The message severity, etc is controlled by ASE and the client is just following suit according to the TDS spec. Its just lacking in the client docs. This can be remedied.
ASE does provide the option to allow truncation and not abort.  It's a set command:
Enter a query:
1 > set arithabort numeric_truncation off
Enter a query:
1 > INSERT dbo.TARGET (S_Name_NVARCHAR,S_RedComponent_DEC_15_6,S_BlueComponent_DEC_12_2,S_GreenComponent_DEC_18_10) SELECT LEFT( S.Name_NVARCHAR,8000),S.GreenComponent_DEC,S.GreenComponent_DEC,S.GreenComponent_DEC FROM (SELECT * FROM SOURCE
) S
4 rows Affected.
Notice though ASE does NOT send truncation message. This is when it is well known and accepted to insert and truncate the numeric data.
Cheers,
-Paul