Strange problem with Search function my wordpress site

It works, but I noticed that some words does not apply to the search function even if the words are in the same posts as other tags and words that are working.

For example: Steins Gate, Gate, Steins, corpse are not working. The tags are working, but the search function for those words give me 0 results. But for example if I write wallenstein, that word works, but not stein. Are there ghost in my wordpress site or what is going on? xD