10.9.3 on iMac 27", dock displays near middle of screen, desktop picture isn't covering whole desktop. Anyone else having this annoying glitch?

Hello Everyone.

I upgraded an iMac 27" (3.4 Ghz, Intel Core i7, 3TB fusion) from Mac OS X 10.8.6., to Mac OS X 10.9.3 a few days back.

Ever since then, the 2nd user to login on a given day, gets the dock displayed near the middle of the screen. It still interacts OK (e.g. you can launch applications from there), but it is not in it's correct location. The desktop picture (in this case, a shade of solid dark grey), only covers the smaller desktop area (up to where the Dock is). The remaining area of the screen automatically gets a 'light grey' background colour.

So person A logs in, no problem. But when person B comes along (with perosn A still logged in), the user logins, and they get this 'chopped of' version of the screen, with the dock mid-screen. (See screenshot attached).

The users can still click on any dock icons, and the applications will open up. But the dock won't return to it's original home, and refuses to 'jump' back to their proper home (at the bottom of the screen).

I've tried using CSCREEN to change the resolution at startup, via a terminal command and Automator, but that only works on some occasions. Others (like the attached screenshot) boot with the two-colour background, and 'confused' dock. A manual screen resolution change in the Settings area (down and then back up again), resolves the issue for that boot.

I've tried stripping back all non-essential plug-ins, tried removing a variety of start-up items, add-ons etc. I've tried creating a 'test' account, and the same issues appear to this account too.

Is it just me, or are others having problems with a misbehaving dock / screen resolution, in Mac OS X 10.9.3 / on an iMac 27"?

Thank you!

D.