Recently I have discovered that the admin menu within WordPress was acting a bit strange. The menu would break and menu items would fall out of place if you hover the mouse above them.
It would seem this is a fault with Google Chrome and not with WordPress itself.
If anyone else is experiencing this issue, there is a temporary fix until Google releases a patch in the next version of Google Chrome (release 47 apparently).
The current workaround is to disable the “Slimming Paint” within the chrome software.
In order to apply the temporary fix you need to enter this URL in your Chrome browser:
chrome://flags/#disable-slimming-paint
Then make sure the slimming paint option is set to enable (i.e. it says disable) and any other entries referring to Enable slimming paint are set to disable (i.e. the option says enable)

See screenshot as this is self explanatory.