I observe with some PDFs, that Viewer 6.3.2 does not highlight the beginning of search result at least in two cases:
1) search result encompasses line break;
2) there is more than 1 space between two words in search result.

Unfortunately, I cannot upload those PDFs because of copyright restrictions, but I created equivalent PDF in LibreOffice (see test_pdf.pdf attached). I made intentionally three and two spaces in a row in the first line.

This looks like a regression since 6.3.0, see comparison screenshots attached.

Steps to reproduce:
1) Open test_pdf.pdf in Viewer RI.
2) Navigate to Search pane (Ctrl + F).
3) Type "sunt explicabo", click "Search" button and observe results.

Actual behavior:
"explicabo" is highlighted (see case1.png attached).
Expected behavior:
"sunt explicabo" should be highlighted.

Note: Similar issue appears when searching for:
1) "modi tempora incidunt ut labore" (see case1_2.png attached)
2) "voluptatem accusantium" (see case2.png attached)
3) "doloremque laudantium" (see case3.png attached)