When dragging a file into a new ark window and choosing a .tar.gz filename to save as, ark goes mad writing things to stdout (i.e. .xsession-errors). Closing the window doesn't stop it.
I think you are misusing ark: you can only drop .tar.gz files into ark. I just verified that this works. Dropping other kinds of files really screws it up though, and we won't be fixing this, as ark has been rewritten from the ground up for KDE 2.