Say I set up a Next/Previous relationship between posts 5 and 7. Assume that 6 winds up with the default post relations. So I think we would have have:
5 <--> 7
5 <-- 6 --> 7
Then if someone merely changes the tags of post 6, doesn't that wind up breaking the Next/Previous relations between 5 and 7?
I've noticed this problem crop up several times. It seems that the code blindly applies whatever is in the Next and Previous fields, even if only the tags were changed.
I just tested this out with post #209715. It used to point to post #209718. However, when I went to post #209716 and merely clicked "Save", the connection between 209175 and 209718 was broken. Now 209715's Next is 209716. (Although 209718's Previous is still 209715.)
I went ahead and opened a ticket #227.
Updated