Hi Rohit,
how you fill in the drop down? try to make simple scenario - data source and crosstab. is this issue occuring also there? Also, if you use BW as data source, you can see in SM04 transaction the sessions in backend. check if the user names are correct, perhaps you have some issues in user mapping on your connection.
if one user does not see what he should - it can actually only mean that this user is connected to the backend with wrong user name - or you have some user exits which are coded on query name and in design studio case the context is different.
Karol