I have a diplo buff (Care and Dedication) that increases Finishing Skills by +15. On the Crafting Skiills tab, the Parent Finishing Skill, in my case Material Finishing (Outfitter) shows a negative number for the sklll value. I'm currently maxxed out at my current level, so it shouldn't show anything. The 3 subskills (Station, Tools, Utilities) are all showing the enhanced values, which it think might be why the Finishing Parent is reporting negative.
I've seen this same thing on other toons that have diplo buffs that affect crafting.