When searching for "LDD-1060" (K2 item with "LDD" in text, title, and tag), the expected results are found. All related items, articles, etc.
Also, searching for "1060" or "106", I get the same good results.
But searching for "LDD", I get results from standard articles, SEO Glossary items, and Phoca Download items. Not for K2 items!

(Using Joomla! standard search)

Hi. K2 uses MySQL full - text search capabilities. By default the minimum word length in MySQL full - text indexing is 4. In order to change this you need to tweak MySQL. Read more for this at dev.mysql.com/doc/refman/5.1/en/fulltext-fine-tuning.html.