Displaying results in Ad-hoc reports using report builder

I have created a model in order to generate the adhoc reports using SQL server report builder.using the report builder I have designed my own report with the model and ran the report.
Following is my issue:
At present my requirement is to display all the part types that exists in the database for an activity.At the back end the query is working properly(I'm getting all the parttypes for each activity.It is returning 187 rows).But while generating the report at the front end I'm getting only the first parttype for that perticular activity though there are many.So at the back end my result set is around 187 rows where as at front end my result set is only 31 rows.Please help me if you have any idea why backend is giving correct results where as at front end the results are like that.