Dunno if this can be called a bug, but is certainly something the XF devs have overlooked. I use the ACP search mainly for quick access to style properties. For example if I want to edit the body I just type "body" in the search field and immediately get results. Problem is if I want to search for the "h1" style property it doesn't work because the ACP search only accepts a minimum of 3 characters. The minimum character amount the ACP search accepts should always match the smallest amount of characters of a style property, phrase or template.