Attachments would not sync across devices

If I create e.g. an Excel file on my desktop as an attachment to one of my notes, initially, it propagates just fine across all my portable devices (a phone and an Android pad).

Now I make some changes to the Excel file (input some new data) on my desktop, save the changed file as prompted by Joplin, and sync the changes across my other devices. And the changes would not propagate. When I open the attached file on my phone or pad, I can see that the file remains as it had been initially synced with no changes accounted for.

Is it something that I am doing wrong here? Or maybe it is some intended logic of Joplin of which I am not aware?

No misunderstanding on your part, this is the current behavior of Joplin. There is a feature request open on GitHub suggesting the behaviour you want. If you give the first comment a thumbs up it will bring more attention to it.