In DS9 "Rejoined" we learn that Trills must not pursue romantic relationships with people their former hosts had romantic relationships with. The reason for this rule is that the symbiont transfer is all about experiencing new things in life. Trills who don't obey this rule are excluded from Trill society, so this is a very strict and important rule.
So what's wrong with Ezri?
At first she doesn't pursue the relationship with Worf because he ignores her - not because of some rule. Than she doesn't do it because she has a little crush on Bashir and started to dislike Klingon stuff. In "Penumbra" finally she overcomes those minor reasons against a relationship with Worf, appears to be completely oblivious to the major reason (exclusion from Trill society) and they "re-consummate" their marriage. Even later, when they broke up again, not a word about the rule.
Now we know that Curzon was more interested in women than in rules, so this might be why Ezri Dax doesn't care. Joran has no interest in rules at all. Does she come back on this topic to explain it somewhere?
Or was the rule suspended (and if so, in which episode)? Or was Ezri simply not informed about that rule since she did not undergo the preparation procedure? Does she have to suffer consequences for her re-consummation (again: if so, in which episode)?