The SvgExporter opens a "group" for some entities, but never closes that group. The resulting nesting can get quite deep and does not conform to the original. I tentatively patched the script as below:

--- SvgExporter.js-orig	2011-05-23 10:55:17.239998578 +0200
+++ SvgExporter.js	2011-05-23 10:55:17.239998578 +0200
@@ -226,6 +226,11 @@
 //        RFileExporterAdapter.prototype.exportEntity.call(this, this.realEntity
 //                .data(), false);
 //    }
+    
+    // dimensions and block references are grouped, close the group tag here
+    if (isDimension(entity) || isBlockReferenceEntity(entity)) {
+        this.writeEndElement();
+    }
 };
 
 SvgExporter.prototype.endEntity = function() {

There might be a better way, but that is what I came up with on short notice.