Thanks Adrian for your explanations.
I agree that playing with files in the .bc folder is not considered as normal operation, but I only did that for bypassing your argument that Cloud synchronizing was not *immediate* as you said.
I again used the Cloud sync on 2 Macs, and unless I do reload the destination Finder folder or use my little script, modification does *not* show dynamically.
I agree with you that it comes from Finder or OSXFUSE, most probably. However, it is very important that this issue be resolved, as the dynamic modification on all the machines is a key feature that works perfectly under Windows but obviously not under OS X.
The user Dede has had the same problem, and from my side, I am able to reproduce it *every time* on any of my 4 macs that I sync with DropBox and BoxCryptor. Even 15 minutes after the modification, it does not replicate dynamically on the other machine's Finder, unless I close and reopen Finder, or use my script....
I can see in the .bc directory that the modification appears immediately, but not on the visible directory.