When using browse to narrow down a search, if two (or more) identically-named items are in the list of terms the term will only appear once.
For example, if narrowing a search by place there are multiple Yorks listed (e.g., the one in the United Kingdom, the one in Ontario, the medieval Viking kingdom, etc), the term "York" will only appear on the list once, and will only point to one of the terms. Murphy's law being what it is, the term used will of course invariably be one of the ones the user didn't intend.
The obvious and simple workaround is just to disambiguate the names. However, this may not be possible sometimes with some datasets for whatever reason, and there isn't an indication that a name pileup is going on unless someone gets suspicious enough to check the affected/suppressed records directly.