Different Results With Sproc As Opposed To Simple SELECT (parameter Values)

Could someone please tell me why the following SELECT statement...

SELECT ID, SpecimenNr, ScientificName, Locality, TaxonFROM petrander.QueryViewWHERE (InstitutionCode = 1) AND (Collectioncode = 1) AND (ScientificName LIKE N'%le%') AND (Locality LIKE N'%Fakse%') AND (22 IN (ParentID1, ParentID2, ParentID3, ParentID4, ParentID5, ParentID6, ParentID7, ParentID8))

...gives me 9 rows back, but embedding the exact same statement in the following sproc...
set ANSI_NULLS ONset QUOTED_IDENTIFIER ONGOALTER PROCEDURE [petrander].[DynamicQuery] @taxparent int = NULL, @museum int = NULL, @collection int = NULL, @binomen Nvarchar(254) = NULL, @locality Nvarchar(254) = NULLAS SELECT ID, SpecimenNr, ScientificName, Locality, Taxon FROM QueryView WHERE InstitutionCode = COALESCE(@museum, InstitutionCode) AND CollectionCode = COALESCE(@collection, CollectionCode) AND ScientificName LIKE 'N%' + @binomen + '%' AND Locality LIKE 'N%' + @locality + '%' AND (@taxparent IN (ParentID1, ParentID2, ParentID3, ParentID4, ParentID5, ParentID6, ParentID7, ParentID8))

...and passing the exact same parameter values to with the following execute statement...

USE [Geomusdb]
GO

DECLARE @return_value int

EXEC @return_value = [petrander].[DynamicQuery]
@museum = 1,
@collection = 1,
@binomen = N'le',
@locality = N'Fakse'

SELECT 'Return Value' = @return_value

GO

gives me 0 rows!? What is different!?

Any help is greatly appreciated...