If you do a search in the catalog, you need to make sure you are selected on the "ALL" button on the "Browse by Category" side (right hand side), otherwise it will only search the specific catalog category you have selected. If you then go to a category, while you still have that search feature, it will try to search and will not show anything.

So, for example, you are on the Agricultural Safety (PS) "Browse by Category" section. You go to "Search Catalog" and search on the word "Mentor" - Mentor will not show up and when you then click on the "Agricultural Safety" section, it won't show anything but it is still trying to search the word "Mentor."

Here's a visual to better explain: