Style Thumbnails Question

[Dave R]

I've been creating a bunch of styles recently and came across a puzzle. I have one style which shows a normal looking thumbnail image in my New Styles library but if I leave it applied to a model, save, close and reopen it, I end up with a different thumbnail. the lines are shown as very thick lines. This wouldn't be a big problem but if I export a JPG of the image, it goes out with the thick lines. Following are some screen grabs related to it. Is there a way to update the thumbnail so this doesn't happen? I've tried updating the style but that doesn't seem to fix it.

In the first image you can see the difference between the In Model thumbnail, the New Styles Library thumbnail--arrows--and you can see a bit of the drawing in the background.

In the second, you can see the results of a JPG export.

And if I reapply the style by clicking on the New Styles thumb, I get this when I do the export.

Any ideas?