Look at the question How do we maintain answer quality when everybody thinks they're experts?.

If I hit Ctrl-D in FireFox this is what it proposes as link text:

content curation - How do we maintain answer quality when everybody thinks they're experts? - Community Building Stack Exchange

It's obvious that the (first) content-curation tag is prepended to the link text (sanitized to remove the hyphen).

Now look at Advantages to storing content locally vs outsourcing it to a 3rd party.
If I again hit Ctrl-D, this is the proposed link text:

small communities - Advantages to storing content locally vs outsourcing it to a 3rd party - Community Building Stack Exchange

The text of the second tag is prepended.

If you look at the edit history of the first question you see that the tags were never edited. The second question currently has no edit history.

Question: what determines which tag text gets prepended to the proposed hyperlink text?

I have searched here and on meta.stackexchange.com thinking that this question actually belongs over there, but with no results. Actually, this prepending of tags does not happen across SE sites (tested on SO and on meta.SE itself) - for all I know it could be specific to Community Building.