diff --git a/etc/PROBLEMS b/etc/PROBLEMS
index 16521e257dd..36fee69351e 100644
--- a/etc/PROBLEMS
+++ b/etc/PROBLEMS
@@ -1615,6 +1615,18 @@ underlying functionality in plasmashell gets fully disabled as well.
 At least a restart of plasmashell is required for the clipboard
 history to be cleared.
 
+*** XFCE: Selected frame loses focus
+
+This can happen, e.g., in Ediff: when you move between the differences
+by typing into the control frame, input focus unexpectedly switches to
+the buffers where Emacs shows the differences, instead of being left
+in the Ediff control frame.
+
+The reason is a bug in the window manager: it shifts input focus when
+raising a frame.  A workaround is to activate the "focus stealing
+prevention" option of the window manager (in XFCE settings, under
+"window manager tweaks", in the "focus" tab).
+
 *** CDE: Frames may cover dialogs they created when using CDE.
 
 This can happen if you have "Allow Primary Windows On Top" enabled which