I just found a bug that could be listed as urgent, but easily avoidable. It's not gamebreaking, but it can mess up your simulation if you aren't aware of it. Actually, I would say put it in the green category.
When you open up the color editor in the physical properties tab and type in a number that is on the
list of controls (including '1') into any of the color property boxes, it also activates the same thing in the simulation itself.
Example:
1. Select any object
2. go to physical properties tab and open the color editor
3. type a number such as, say, '6' into any of the color options.
4. observe the gravity being set to negative after you click okay.
It is easily avoidable by either simply pausing US so that you can change the gravity back to where it was or just use the target thing and the slider and not type into the color property boxes.