Visual Studio Reporting Services - MultiValue Parameters

[RiddleMeThis]

Hi, I dunno if this is in the correct catagory, hope so, sorry if it's not.

I'm trying to get to grips with SSRS and having a bit of trouble with multi value parameters.
I'm using the following code in the data section:

SELECT AccID, AccName, StartDate 
FROM Account 
WHERE AccID= @prmAccID

This works fine with the default settings, the report prompts me for @prmAccID, so I put in an Account ID and it gives me the relevant name and start date to go with that account.

However if I go to the 'Report > Report Parameters' dialog and check the "Multi-Value" checkbox then try and run the report, it still works if I only put one account ID in at the prompt, but if I put 2 account ID's in I get the following error:

An error occured during local report processing.
An error has occured during report processing.
Query execution failed for data set 'DSAccountRepor t'.
Must declare the scalar variable "@prmAccID" .

Surely it should use the following code if i put in AccID 34 and 35

SELECT AccID, AccName, StartDate 
FROM Account 
WHERE AccID= 34
   OR AccID = 35

[RiddleMeThis]

Just realised the code I should have been using is:

SELECT AccID, AccName, StartDate  
FROM Account  
WHERE AccID IN (@prmAccID)

It doesnt treat it like an OR condition, it treats it like an IN condition and so, with account IDs 34 and 35 for example, it would use the following code:

SELECT AccID, AccName, StartDate  
FROM Account  
WHERE AccID IN (34,35)