Steven, thanks for your reply.
I found out that the behaviour of the search function seems to be a bit more complex:
For example I have several entries (album artists) that start with "Mike Oldfield". The first one simply is "Mike Oldfield", the second one is "Mike Oldfield (Pekka Pojohla), the third one is "Mike Oldfield / Bedford" and so on.
When I begin to type into the search field everything is OK as long as I type the first 3 characters "Mik". The the first entry of the MO-entries is shown and visible.
As soon as I type the fourth character "e" ("Mike") the list scrolls down for one entry so that the first entry "Mike Oldfield" is hidden behind the search field.
This goes on with every additional character I type. The list scrolls down for one entry with every single character I type. Finally - when I have typed in "Mike Oldfield" not the first entry "Mike Oldfield" is the first search result but "Mike Oldfield y Diego Cortes Pastosi" which is the 12th of my album artists that start with "Mike Oldfield ...".