Index: /trunk/src/org/openstreetmap/josm/gui/history/HistoryBrowserDialogManager.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/history/HistoryBrowserDialogManager.java	(revision 16797)
+++ /trunk/src/org/openstreetmap/josm/gui/history/HistoryBrowserDialogManager.java	(revision 16798)
@@ -128,5 +128,5 @@
      */
     public void hideAll() {
-        dialogs.values().forEach(this::hide);
+        new ArrayList<>(dialogs.values()).forEach(this::hide);
     }