Search through Linklist in Richtext field not working?
The reason that searching for Ascot doesn't match sponsorenhochdreiascot is because Craft doesn't do wildcard or fuzzy searching by default.

If you search for *ascot it would match.  You can all of the supported search syntaxes here: http://buildwithcraft.com/docs/searching

Update:
As of Craft 2.5, you can enable fuzzy searching by default.