Duplicate value exception while inserting into an autoincremental-PK table

I recently experienced a SqlCeException: "A duplicate value cannot be inserted into a unique index" while inserting a record in a table (SqlCE 3.5).

It seems the INSERT statement violates the primary key constraint. However, on the relevant table, the PK has been defined as an autoincrementing identity:

[ID] int identity(1,1) NOT NULL,

The exception is not systematical: it happens once in a while.

What could be the cause of this exception?

Doesn't the identity(1,1) guarantee a unique ID for each INSERT, does it?

Could this be a SqlCE bug? If so, how could it be circumvented?

Here is the Exception trace (it explicitly refers to the PK_ID constraint):

System.Data.SqlServerCe.SqlCeException: A duplicate value cannot be inserted into a unique index. [ Table name = HistoricalData,Constraint name = PK_ID ]
  at System.Data.SqlServerCe.SqlCeCommand.ProcessResults(Int32 hr)
  at System.Data.SqlServerCe.SqlCeCommand.ExecuteCommandText(IntPtr& pCursor, Boolean& isBaseTableCursor)
  at System.Data.SqlServerCe.SqlCeCommand.ExecuteCommand(CommandBehavior behavior, String method, ResultSetOptions options)
  at System.Data.SqlServerCe.SqlCeCommand.ExecuteNonQuery()
  at Invensys.Compact.Persistence.SqlCe.PlantData.SaveHistoricalRecord(HistoricalRecord record)
  at ...

Table definition is:

CREATE TABLE [HistoricalData] ( 
[ID] int identity(1,1)  NOT NULL,
1675855251 datetime NOT NULL,
[Type] smallint NOT NULL,
[IDLastAll] int,
[IDRef] int NOT NULL,
[BinaryLength] smallint NOT NULL,
[Data00] varbinary(500),
[Data01] varbinary(500),
[Data02] varbinary(500),
[Data03] varbinary(500),
[Data04] varbinary(500),
[Data05] varbinary(500),
[Data06] varbinary(500),
[Data07] varbinary(500),
[Data08] varbinary(500),
[Data09] varbinary(500));


--  Create Primary Key Constraints 
ALTER TABLE [HistoricalData] ADD CONSTRAINT [PK_ID] 
    PRIMARY KEY ([ID]);

--  Create Indexes 
CREATE INDEX [IDX_Type_Timestamp]
ON [HistoricalData] ([Type] ASC, 1675855251 ASC);

CREATE INDEX [IDX_Timestamp]
ON [HistoricalData] (1675855251 ASC);

The INSERT is performed via a SqlCeCommand. Here is the code (C#):

 _insertRecordCo开发者_开发百科mmand =
     new SqlCeCommand
     {
         Connection = _connection,
         CommandType = CommandType.Text,
         CommandText = HISTORICAL_DATA_INSERT
     };

 _insertRecordCommand.Parameters.Add("@Timestamp", SqlDbType.DateTime);
 _insertRecordCommand.Parameters.Add("@Type", SqlDbType.SmallInt);
 _insertRecordCommand.Parameters.Add("@IDLastAll", SqlDbType.Int);
 _insertRecordCommand.Parameters.Add("@IDRef", SqlDbType.Int);
 _insertRecordCommand.Parameters.Add("@BinaryLength", SqlDbType.Int);

 for (var i = 0; i < DATA_BLOCK_NUMBER; i++)
 {
    _insertRecordCommand.Parameters.Add(DATAPARAMETERNAMES[i], SqlDbType.VarBinary, DATA_BLOCK_SIZE);
 }

 _insertRecordCommand.Prepare();

 // Here the parameters are filled.

 _insertRecordCommand.ExecuteNonQuery();

I left out how parameters are filled. Nevertheless, there is no [ID] (the primary key) parameter.