pkg install via pui-list-packages deletes the pkg, why?

[Uwe Brauer]

Hello

I would like to try out some packages in pre release, and may be go
back to the stable version. 

However when I download manually the package and install it via 
pui-list-packages then the pkg is deleted after installation.

Could that behavior be made optional, that is I would like to keep the
pkg after installation.

thanks

Uwe Brauer