I am about to ask question regarding the above subject when I found out (see links below) didn't solve the problem. Going back and forth windows and wait for some time still won’t show the CustomView. I am using now v9. I think v8.50 still not fixed.
The best work around is either checkmark CustomListView library or xCustomListView library!
Then go to Designer and see under Add View that CustomView already enabled!
Never use both CustomListView and xCustomListView libraries. Only use xCustomListView and make sure that you wait until the version string appears before you switch to the designer.