Graphical bug NSVisualEffectView when app in background

My application has a NSTableView configured as a SourceList. Under the NSTableView are two NSButton two add/remove items in the table. The table and the buttons are embedded in a NSVisualEffectView (.behindWindow mode).

The result is great and I can see the background through the table and the buttons, BUT, when the app is in background (I give the focus to another app), the tableview and the buttons become black, and the view is not redrawn, as shown in the picture below (taken with an iPhone, because a screenshot does not show the bug!):

And here is the IB structure of the views:

The container view (CustomView) is layer-backed.

Any lead to solve this problem? Thanks in advance !

The problem was that I was trying to have a NSOutlineView translucent (Behind-window blending), but under a TabView.

Apple UI guidelines (here) state the following:

Use an opaque background when a window contains more than one sidebar, and when using a sidebar in a panel or preferences window. All other times, use a translucent background.

Because of the TabView, I was clearly against this rule which had technical side effects (which led to this post :-)).

--> making the NSOutlineView opaque (not as a SourceList) solved the problem.