Toggling multi view via keyboard shortcut in separate viewer does not work

I am using C1 (Windows) in a dual monitor setup with separate viewer window. Since version 13.0, toggling the multi view via a keyboard shortcut no longer works in the viewer window. In the main window switching still works, but only there. In the viewer window I can only switch the view by mouse click. All other shortcuts still work (e.g. focus mask...), so it has nothing to do with whether the focus is on the right window.
I opened a support case a year ago, but apparently the problem could not be reproduced. Unfortunately, it didn't improve until version 14.1.
Has anyone else here on this forum experienced this problem or am I the only one?