>I wonder wath can cause such a corruption, would you know?

Yes, abrupt termination over a network when open write-access can cause file corruption of many file types, not just vfp.

Note that DBCs are opened "write-access" even in non-Exclusive mode - they are tables, after all. I have found a fix for that particular problem:

Install all possible DBC/DCT/DCX files in a separate ReadOnly server directory (with admin-only write access). This usually includes most DBCs. Doing this will eliminate any such DBC corruption problems by users.