Hi, I made an account just to comment on this - I am also experiencing this same problem but I've found a temporary workaround. Basically, to get the boxes checked you need to click where the drives are on the right side and then you can use the down arrow key to select the drive(s) - it will automatically check them from top to bottom as you press it. I'll go back after the scan finishes to see if i can deselect drives using other arrow keys or enter.
Just a quick edit, this also only begin occurring to me after Dec. 14 so whichever version I was on then this problem was not occurring.