Install disk won't stay ejected

Hi:

I recently installed a pref pane.  Open the .dmg and mount the installer.

In the past this had  a copy of the pref pane and doing a double click on this copied it to the correct place.  It appears it has done this but every time I log out or restart the install disk remounts.  

Tried removing all trace of the pref pane and then reinstalling by copying rather than double-click but the mounted disk still reappears.

There is obviously a rogue process that keeps re-spawning, but I have no idea which it is or how to kill it for good.  

Any one have any suggestions?

Chris

Mojave 10.14.3