What happens if you recreate the railing from scratch?

stop your tread line at the nosing of the stair, or split at the nosing and let it continue just to the backend of the stair. From the looks of it you are extending the 12" past the back end of the stair, even though your last tread is at the same level as the floor.

Creating the rail from scratch doesn't read the stair's slope and the rail remains horizontal. And the whole idea was to create a family that is usable without tweaking, without path adjustments and height correction.

Yep, splitting the path solves the problem. It can be any distance, as long as it is after the last tread edge. It's a shame that they didn't add 'plus last tread' option to the end of the railing as well.

This is the common goal.

I found Stairs and Railings very challenging until I spend some time with them - a fair bit of time.

I would say your stair Finishes with a Riser. In Revit's mind the Railing needs to continue up another level. This is why it continues to the end of the final tread, rather than finishing at its start. So what you are looking at may be correct.

20170815-Stair1.JPG

Additional stair settings that can be set before you place your stairs can be found in the Properties Dialog. Select New Stairs: Runs. This is a hidden dialog that I did not know was there for the longest time.

20170815-Stair3.JPG

Check out the differences you can get when you check on/off End with Riser.

Regardless, I always adjust my Railings to ensure they are compliant, including putting flat portions on.

20170815-Stair2.JPG

Neither Railings nor Stairs are easy, but stick with it.