Squashed icons...

[Supergrunch]

I have a fairly odd problem with my laptop... basically, every now and then, the icons get subtly squashed up so there is a gap where there shouldn't be... when I restart, this problem corrects itself. It's hard to describe, so I'll show you some screengrabs (apologies for the size).

 

Normal:

 

 

Squashed:

 

 

It's not just that the 6 icons at the bottom have been shifted down, even though they're partially covered by the start bar- if you move them up, there's a large gap underneath. I think the space between the icons must have been reduced.

 

The only things that I think might have caused it is using Tweak UI to change the arrow in the corner of shortcuts, and manually changing some of the icons... but surely neither of those should cause this to happen...

 

This is happening more and more, so does anyone know how I can make it stop?