One quest from the pony Minister Spindle from Crystal Empire is bugged. It shows the exclamation mark over her head and on minimap after I completed the quest too. And I still have her quest in the book, it keeps reopening everytime I teleport in another location. I tried completing it in all possibilities getting the rewards everytime but it keeps happening and it annoys me because it's stuck in my quest book.
The objective marker issue has a fix now. Go see Old Quest Marker Fix by the Cantermore train station and select the option for Letter of the Law. He should cancel the objective marker for you. This will be effective after the next server reset.