CVS generates new files

[Rasmus Resen Amossen]

cvs has began to generate new files when I run "cvs update" or "cvs
checkin".

Fx. I have a file, "helloworld" in version 1.7 in my working catalog,
and the file is newer on the server. When I run "cvs update", the file
"helloworld" is beeing merged with the file on the server, but the old
version (1.7) is copied to a new file automatically: "helloworld.~1.7~"
(in my working catalog).

Also when I checkin the "helloworld" file, a new file is generated in my
working catalog: "helloworld.~1.7.~". 

Why that? I don't want all these extra files. How can I avoid them?
I use Redhat7.3, cvs-1.11.1p1-7, xinetd.

Thanks!

Rasmus