This probably will fix the issue:
diff --git a/program/js/editor.js b/program/js/editor.js
index 829373a..3fc5698 100644
--- a/program/js/editor.js
+++ b/program/js/editor.js
@@ -129,6 +129,15 @@ function rcube_text_editor(config, id)
return;
}
.
+ var area = $('#' + this.id),
+ height = $('div.mce-toolbar-grp:first', area.parent()).height();
+
+ // the editor might be still not fully loaded, making the editing area
+ // inaccessible, wait and try again
+ if (height > 200 || height > area.height()) {
+ return setTimeout(function () { ref.init_callback(event); }, 300);
+ }
+
var css = {},
elem = rcube_find_object('_from'),
fe = rcmail.env.compose_focus_elem;