Steps to Reproduce:

1. Create a new page
2. Type, for example Test then hit Shift + Enter, that should go to the next line.
3. Type atlassian save that, and do a reindex.
4. Go to your search box, and search for Test, you'll see that you won't find anything.
5. Now try to type Testatlassian, you'll see that it works.

Here is the Storage page:

<p>Test<br />atlassian</p>

Probably Lucene is not understanding the HTML code <br />

Workaround:

Instead of using Shift + Enter, press just Enter.