There are a couple reasons for this. When you click on the hint and it is shown as being attached to someone else. I have found that sometimes the source had been attached to the wrong person and I've detached it. At other times it has been attached to possibly the same person with a different ID. In that case, after checking the record very carefully, I would merge the two records. I have found many duplicates through this process.
Hope this helps some,
Following on what 'Carol' has already proffered ...
Sometimes, by the time you see it/'get around to it' the "Hint" has ALREADY been attached by another User/Patrons.
As an aside ...
IF, you are referring to the "Hints" that you can see in some of the many "Campaigns"; THEN, part of the problem/issue is that those "Campaigns" are "Refreshed", every so often, it is on 'immediate'.
I have seen ALL of the "Hints" in some of the various "Campaigns" as being attached; and, I know; as, I was the one that attached them, 'many moons ago'...
As long as the "Hint" (ie, "Source") is correctly attached to the right individual/person, do not worry about it, be thankful that it is attached, no matter by whom - just move onto the next one.
Just my thoughts.