Seems WordPress 2.6 reworked the CSS and such for the widgets page in order to fix the issues that had been occurring with widgets not dropping into the right order. However that means the widget editor screen of my plugin is now broken and it was now just pointed out to me.

I’ll try to update as soon as I can and eventually see if I can just resort to making it so you edit the dashboard via Design -> Widgets like I should have done in the first place.