Thanks Noel but it is definitely happening to me. Not every time but definitely once or more in every session. I suspect if you try this several times it will happen to you as well.

1) click and drag to select a few bars
2) with those bars selected right-click on the first selected bar
3) sometimes this will cause everything that was selected to be deselected

As I said this is not new to 2018...it has been there with 2017. And it is not unique to my setup. I just tried it twice on my old computer running BIAB 2017 build 463 and the first time it was fine and the second time it deselected bars.