The DATEX Tool aleady contains a feature to deselect attributes of ‘DataValue’. That was because ‘DataValue’ is never traversed in the tree from top down, but only from inheriting components. Now consider a similar structure, where some class is located in the same way as DataValue (i.e. no associations from 'the top'), but has got additional associations itself. They will never be reached within the tree, and therefore they are not displayed. Thus you cannot select or deselect them. This might be some special case; it might have to be discussed, if the tool should be capable of this. Anyway it is possible to find an alternative (but not exactly same) modeling structure for this. In the moment it is not possible to attach files here; I sent some source files for this feauture request to Jonas Jäderberg.
Please refer to the picture above (x.png).
Changed to bug.
Solved this by introduced a new meny item when you right click on the list of "Members". If its a relation you will get an option to select "Target members" which will open up a "Members" dialog for the target class.
Will be released in version 2.3