In terms of not performing what the user might expect from search behaviour, an example I found was the following:

A word "elasticlunr", appears in the linked article, and the linked article appears in search results, but searching any partial string such as "elastic", "elasticl" "elasticlu" and "elasticlun" will not result in finding the linked article. Perhaps this behaviour is intended by the author, but it may not be intended by the various users of the site.

Oddly,

> elastic* and elasticl*

does find the linked article, but

> elasticlu* and elasticlun*

do not.