What the heck is happening with this Linq-to-SQL query? - linq-to-sql

Question

[Resolved - see update]
I have this L2S query (looks scary, but the bit that's going wrong is simple):
var historicDataPointValues = from dpv in this._dataContext.DataPointValues
where (dpv.categoryId == historicCategoryId)
&& (dpv.retailerId == historicRetailerId)
&& (dpv.questionId == question.PreviousQuestionId)
&& historicResponseIds.Contains(dpv.responseIndex)
&& ((dpv.dataPointIndex == firstDataPointIndex) || (dpv.dataPointIndex == secondDataPointIndex))
select new KeyValuePair<string, double>(MakeDataPointValueKey(dpv), dpv.value);
...which was producing no results, so I looked at the SQL emitted by L2S.
When I execute it, the value of firstDataPointIndex is 1 and secondDataPointIndex is null. Yet the query that L2S produces (as shown in the debugger) is:
SELECT [t0].[categoryId], [t0].[retailerId], [t0].[questionId], [t0].[responseIndex], [t0].[dataPointIndex], [t0].[value]
FROM [dbo].[DataPointValue] AS [t0]
WHERE ([t0].[categoryId] = 1)
AND ([t0].[retailerId] = 1)
AND (([t0].[questionId]) = 8)
AND ([t0].[responseIndex] IN (1, 3, 4, 5, 6, 7, 8, 10, 11, 12))
AND (([t0].[dataPointIndex] = 13) OR ((CONVERT(Int,[t0].[dataPointIndex])) = 14))
Note the values 13 & 14 where firstDataPointIndex and secondDataPointIndex should be (they should be 1 and NULL; if I put in the correct values, then I get the results I expect).
WTF?
UPDATE: Turns out that the L2S debugger was at fault. It wasn't showing the same SQL as what's actually sent to the server, which is:
exec sp_executesql N'SELECT [t0].[categoryId], [t0].[retailerId], [t0].[questionId], [t0].[responseIndex], [t0].[dataPointIndex], [t0].[value]
FROM [dbo].[DataPointValue] AS [t0]
WHERE ([t0].[categoryId] = #p0) AND ([t0].[retailerId] = #p1) AND (([t0].[questionId]) = #p2) AND ([t0].[responseIndex] IN (#p3, #p4, #p5, #p6, #p7, #p8, #p9, #p10, #p11, #p12)) AND (([t0].[dataPointIndex] = #p13) OR ((CONVERT(Int,[t0].[dataPointIndex])) = #p14))',N'#p0 int,#p1 int,#p2 int,#p3 int,#p4 int,#p5 int,#p6 int,#p7 int,#p8 int,#p9 int,#p10 int,#p11 int,#p12 int,#p13 int,#p14 int',#p0=1,#p1=1,#p2=8,#p3=1,#p4=3,#p5=4,#p6=5,#p7=6,#p8=7,#p9=8,#p10=9,#p11=10,#p12=11,#p13=1,#p14=NULL
Note that the query now contains #p13 and #p14 where previously it had scalar values.