Index: openacs-4/packages/acs-tcl/tcl/utilities-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-tcl/tcl/utilities-procs.tcl,v
diff -u -N -r1.140.2.75 -r1.140.2.76
--- openacs-4/packages/acs-tcl/tcl/utilities-procs.tcl	24 Apr 2017 15:53:45 -0000	1.140.2.75
+++ openacs-4/packages/acs-tcl/tcl/utilities-procs.tcl	24 Apr 2017 18:39:29 -0000	1.140.2.76
@@ -550,7 +550,7 @@
     -entire_form:boolean
     -no_empty:boolean
     {-base}
-    -base_encode:boolean
+    -no_base_encode:boolean
     {-anchor}
     {-exclude {}}
     {-override {}}
@@ -695,8 +695,8 @@
     along with a question mark (?), if the query is non-empty. so the returned
     string can be used directly in a link. This is only relevant to URL export.
 
-    @option base_encode Decides whether argument passed as <code>base</code> option will be
-                        encoded by ad_urlencode_url proc
+    @option no_base_encode Decides whether argument passed as <code>base</code> option will be
+                           encoded by ad_urlencode_url proc
 
     @author Lars Pind (lars@pinds.com)
     @creation-date December 7, 2000
@@ -932,17 +932,24 @@
     if { $quotehtml_p } {
         set export_string [ns_quotehtml $export_string]
     }
-    
+
     # Prepend with the base URL
     if { [info exists base] && $base ne "" } {
-        # if required, encode url part as well
-        if {$base_encode_p} {
-            set base [ad_urlencode_url $base]
+        if { [string first ? $base] > -1 } {
+            # The base already has query vars; assume that the
+            # path up to this point is already correctly encoded.
+            set export_string $base[expr {$export_string ne "" ? "&$export_string" : ""}]
+        } else {
+            # The base has no query vars: encode url part if not
+            # explicitly said otherwise. Include also as exception
+            # trivial case of the base being the dummy url '#'.
+            if {!$no_base_encode_p && $base ne "#"} {
+                set base [ad_urlencode_url $base]
+            }
+            set export_string $base[expr {$export_string ne "" ? "?$export_string" : ""}]
         }
-
-        set export_string $base[expr {[string first ? $base] > -1 ? "&" : "?"}]$export_string
     }
-    
+
     # Append anchor
     if { [info exists anchor] && $anchor ne "" } {
         append export_string "\#$anchor"