Interchange Assembly not replacing in Main Assembly

Hi,

We've created an Interchange assembly consisting of 3 assemblies which are being interchanged according to some condition in top level assembly. Although Interchange Assembly is in session, the replacement is not happening in top level when we open an instance of top level assembly separately. But if we open & regenerate Interchange Assembly, replacement will happen. But this is not what we need. We need replacement to happen at first itself. Any solutions will be appreciated.

Thanks