This is normal. The same thing happens with fanart and fan images, when you browse through the gallery bit-by-bit when using the 'previous' and 'next' button deactivated works will also come up.
When a fan work (in this case character) is deactivated it will only be removed from the list, but when you search up a character's name they will still appear. As Dollyshewolf said, they will only be completely gone if the user deactivates their character.

No it can't be changed only if the character is deleted it will no longer show up and the character can only be deleted by it's owner so if they choose not to delete it then it won't be removed from the search.

no software/programming is perfect.
and no it cannot be stopped. if you type in that name then any characters - including deactivated ones, will show up on your page. your computer takes in the basics and returns all results so to speak