You may see this happen if your Dock is wide and you've got Butler's hot corners enabled: icons will be located near the bottom right corner of the screen, so Butler's hot corner will activate as you drag something down to the trash. (The same would apply for long vertically-oriented Docks.)

To fix this, disable the bottom right (or hot corner closest to your Dock's edge) hot corner in Butler's preferences. Select Butler > Preferences from the Butler menu bar icon, then select Editing. Uncheck any/all you don't want to use, and the problem should go away.