I think nostr:npub12vkcxr0luzwp8e673v29eqjhrr7p9vqq8asav85swaepclllj09sylpugg cashing relay helps here. 

Not sure about how other apps do it. But I have a feeling that they do download redundant notes. 

Unless the app refreshes the filter parameters after each incoming note? 

But it must be media that creates this issue, not text notes even if there were redundant downloads.