link (shift+f1) a mistery and a danger

a mistery:
if I link (shift+f1, link) an object , then I append (shift+f1, append) another object from the same donor file, then the first linked object became editable. This doesn’t happen if I append the second object from a different donor file

A risk:
If I link an object and I delete , rename or move the donor file, then the receiving file is LOST forever.
This is really too dangerous

If you can’t handle it, don’t use it. A bit like matches.

another discovery:
you can modify linked object by the Trasnform properties palette.

It will be very useful to use the link, but the risk of loosing my files…