First time in Blackmarsh I just gathered 4 crimson nirnroots and picked up Sinderion's journal, getting the "A Return to your Roots" quest to find out about the plant. Unfortunately, I did not read Sinderion's journal until after I left. When I did read the book, the quest updated to finding 30 of the plants. Fine. I put the 4 I collected in my Alchemy stash thinking I would go back to Blackmarsh and find 30 new ones. But the quest updated by telling me I now had -3/30 crimson nirnroots. Back in Black marsh, I found 23 more and returned home to add the 4 I found and it tells me I have 30 (but I really only have 27). When I go to drop off the "30" at the farm, there is no dialog for the quest.
I am thinking when I actually do get 30 I may have to reset the quest with the console.
It is not game breaking , but I wanted to put this out there and see if anyone else had a similar experience.