I have had this problem ever since the new Webmail came on stream. I don't use preview pane. Was hoping your solution would work for me but it doesn't as I don't have Settings visible anywhere!
Just replied couldn't find Settings at top left of screen to turn this off, but have now found Settings when I click on my user name at the top RIGHT of the screen and yes, there is an item to turn off after delete. Fixed now that goodness!
