I've come across something rather odd. 
I am reporting it here, but will try and see if I can reproduce the issue on a regular basis if I can.
Ok, I actually just managed to do it. Often, if I use Shift+Space to go to the next line, I find that the space bar suddenly stops working (This seems to occur on the 3rd time I use the Shift+Space - so the third line).

Looking into this a bit further, it's fine if I use a standard carriage return (like to this paragraph). It also seems to be if I press Space Bar, BEFORE I start typing, it will jump me back to the previous line. 
By no means game-breaking, but can be annoying.
Likethislinehere.ThethirdShift+Spaceperparagraphhasstoppedmyspacebarworking.

But if I do a normal return, the space bar works again.

Weird. :-)