Index: trunk/src/org/openstreetmap/josm/data/validation/tests/UnclosedWays.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/validation/tests/UnclosedWays.java	(revision 17488)
+++ trunk/src/org/openstreetmap/josm/data/validation/tests/UnclosedWays.java	(revision 17489)
@@ -96,5 +96,12 @@
             String value = w.get(key);
             if (isValueErroneous(value)) {
-                return TestError.builder(test, Severity.WARNING, code)
+                final Severity severity;
+                // see #20455: raise severity to error when we are sure that tag key must describe an area
+                if (ignore && !specialValues.isEmpty()) {
+                    severity = Severity.WARNING;
+                } else {
+                    severity = Severity.ERROR;
+                }
+                return TestError.builder(test, severity, code)
                         .message(tr("Unclosed way"), engMessage, engMessage.contains("{0}") ? new Object[]{value} : new Object[]{})
                         .primitives(w)