no... not even close to "5"... my hand is always on "shift" and "s"... other hand on mouse... ;P

i can see its something different that is happening. pressing 5 goes to "advance mode" and pressing again goes back... using undo does not do anything.

when this happened to me (about 4 times now, in the middle of dragging the beginning of a event), undo messes up everything...

really weird...

Is this supposed to be a 3D project? It looks like your project is set for "3D Side-by-side Full" mode in youre first screen shot -- or at least I can get my (non-3D) project to look like that if I mess around with the project properties.

Your track is set to "Expand Track Layers" (or did you already know that?)
(Edit: Ooops -- you already knew that...)

Edit #2: 3D properties can also be set in the MEDIA properties of a clip -- even if the project isn't set for 3D. If you select an event, right-click and chose Properties, select the Media tab, and set the Stereoscopic 3D to "Top-Bottom Full" (at very bottom of the media tab), you'll get the skinny, stretched out picture like your second screenshot -- even if your project properties aren't set for 3D. Maybe there is a keyboard shortcut that does this and you accidentally found it? (or maybe a bug?)