So, apparently I'm the first with this problem; I assume so because I've yet to find any mention of this particular bug.
I started this quest on a bit of a rough note as it is. I had to leave the jail and re-enter to get Sinding to even approach the bars. But once he did, all went well. He gave me the ring, transformed and fled from the cell. Now, I was doing another side-mission in the area of Falkreath before heading off to the nearest location I could fast-travel to near Bloated Man's Grotto. I entered, and spoke to the dying Hunter. Then I got the quest update to kill Sinding, but the marker indicated he was roaming out in the forest. So, I found him, but accidentally exited the dialog before I could tell him whether I was going to help him or not. This resulted in him fleeing to the Grotto where the quest continued as normal.
Now, I don't want the Savior's Hide armour, I wanted the Ring of Hircine. So I loaded my last (and only) save. I figured if it glitched similarly, I could just make sure not to exit the dialog with Sinding before telling him I was on his side. But, the bug has changed somehow. NOW instead of roaming the world aimlessly, waiting for me to find him, the quest marker indicates he's in the jail cell. Here is where the bug is different from any I've looked up. The MARKER is in the cell, but Sinding HIMSELF is NOT.
I've reloaded, and reloaded, and reloaded, changing the path I take to the Grotto and such (even choosing not to do the side-mission I mentioned earlier), all to only have the marker indicate the middle of the Falkreath jail cell everytime since. I have no idea what to do, as now I'm simply stuck with the damned Curse Ring of Hircine.