I am using build 18 and I run into either a bug, or an undocumented change in behavior (but a change for the worse, in my view).
I am using the Explorer plugin in Theater View to navigate to folders with video files in them. I navigate to the folder where the file I want to play is located, and then I move the cursor over the file I want to play with the keyboard "down arrow" key, and press the "Play" key combination (Ctrl+P) or press the keyboard Play/Pause media key when the cursor is over it.
What used to happen was that the file under the cursor started to play.
What happens now is that the first video file in the folder I am in starts to play always, no matter which file I have under the cursor!
I noticed that I have to enter the file itself and press "Play" if I want to play it. This should not be necessary.