Indeed, according the documentation the search should be disabled when the property 'editable' is enabled. Beside the documentation I don't find a change in any release notes of each Mendix 6 version. I've tested it in a project of my own which is in Mendix 6.10.2 and Mendix 6.10.3. The behavior of the listview is equal to the documentation. Retrieving the data by database or XPath doesn't change the behavior.
Some questions:
I think you should report the issue at Mendix, but maybe it's difficult to reproduce the issue in a test project.