Sudden file permissions change.

It is the second time within a couple of months I notice a
sudden file permission change.
A file with the -rw-rw-r– pattern gets the -rwx------ one
during a routine copy procedure. The ownership and the group
remain intact.

QNX v4.25G
TCP/IP v5.0

What may be the cause?

A third incident was very long ago with a directory being turned into a regular file…