diff --git a/resources/compiled_coffeescript.zip b/resources/compiled_coffeescript.zip
index bb4bee87f8..6a24d85b2a 100644
Binary files a/resources/compiled_coffeescript.zip and b/resources/compiled_coffeescript.zip differ
diff --git a/src/calibre/ebooks/oeb/display/paged.coffee b/src/calibre/ebooks/oeb/display/paged.coffee
index 5fb8346540..39c7dc28e7 100644
--- a/src/calibre/ebooks/oeb/display/paged.coffee
+++ b/src/calibre/ebooks/oeb/display/paged.coffee
@@ -161,7 +161,7 @@ class PagedDisplay
         # The location of the left edge of the left most column currently
         # visible in the viewport
         x = window.pageXOffset + Math.max(10, this.current_margin_side)
-        edge = Math.floor(x/this.page_width)
+        edge = Math.floor(x/this.page_width) * this.page_width
         while edge < x
             edge += this.page_width
         return edge - this.page_width
@@ -237,6 +237,18 @@ class PagedDisplay
             # selection
             this.scroll_to_xpos(left+5)
 
+    jump_to_cfi: (cfi) ->
+        # Jump to the position indicated by the specified conformal fragment
+        # indicator (requires the cfi.coffee library). When in paged mode, the
+        # scroll is performed so that the column containing the position
+        # pointed to by the cfi is the left most column in the viewport
+        window.cfi.scroll_to(cfi, (x, y) =>
+            if this.in_paged_mode
+                this.scroll_to_xpos(x)
+            else
+                window.scrollTo(0, y)
+        )
+
 if window?
     window.paged_display = new PagedDisplay()
 
diff --git a/src/calibre/gui2/viewer/position.py b/src/calibre/gui2/viewer/position.py
index 99cd634a21..d213443388 100644
--- a/src/calibre/gui2/viewer/position.py
+++ b/src/calibre/gui2/viewer/position.py
@@ -37,17 +37,8 @@ class PagePosition(object):
     def scroll_to_cfi(self, cfi):
         if cfi:
             cfi = json.dumps(cfi)
-            self.document.mainFrame().evaluateJavaScript('''
-                    function fix_scroll() {
-                        /* cfi.scroll_to() uses scrollIntoView() which can result
-                           in scrolling along the x-axis. So we
-                           explicitly scroll to x=0.
-                        */
-                       scrollTo(0, window.pageYOffset)
-                    }
-
-                    window.cfi.scroll_to(%s, fix_scroll);
-                '''%cfi)
+            self.document.mainFrame().evaluateJavaScript(
+                    'paged_display.jump_to_cfi(%s)'%cfi)
 
     @property
     def current_pos(self):
diff --git a/src/calibre/library/prefs.py b/src/calibre/library/prefs.py
index 8b2bb0c7fd..4bd39e20b2 100644
--- a/src/calibre/library/prefs.py
+++ b/src/calibre/library/prefs.py
@@ -65,6 +65,9 @@ class DBPrefs(dict):
             return default
 
     def set_namespaced(self, namespace, key, val):
+        if u':' in key: raise KeyError('Colons are not allowed in keys')
+        if u':' in namespace: raise KeyError('Colons are not allowed in'
+                ' the namespace')
         key = u'namespaced:%s:%s'%(namespace, key)
         self[key] = val