Layer Style Preview broken

[ThatRobHuman]

The layer-style dialog breaks preview of a layer.

The red vector layer is the layer that I'm editing the layer styles on:

The actual image:

While the layer style dialog is open:

[ThatRobHuman]

Now this is happening whenever I change the layer in question. All blending falls apart until I hide and unhide the layer.

[ThatRobHuman]

and here's what it's like drawing new vectors....

[ThatRobHuman]

For additional clarity: My system is not overloaded and this has only just recently started up. Yes, I've reset my preferences, again. Yes, I'm on the latest drivers for everything.