We recently upgraded from DNN 7 to DNN 8 and have been experiencing quirky behavior here and there.  One bug we encountered recently involved a particular module on a page while in edit mode and the Publish bar at the bottom disappearing. 

 This bug was discovered by putting a page in edit mode and then adding our custom module to the page.  The module uses knockout js and the jquery ui widget factory.  As soon as the module is put on a page, the publish bar disappears and we receive a 404 error in the console for edit-bar.html GET /undefined/EditBar/Html/edit-bar.html 404 (Not Found) . Due to the undefined path, we assumed it was JS related.  We couldn't find anything in our code that would conflict with DNN's code.  We traced it back to dnn.js and the getVar/getVars functions.  When it calls getVars, the dnn.vars variable isn't null, its an empty object...so it's never initialized from the hidden input.  When the page loads, the variable IS null...so we did our best to track down where this variable changes.  Not sure where it's SUPPOSED to be initialized initially, but it appears the object stops being null right when the jQuery Widget is being created.  So it appears something with jQuery's Widget Factory is conflicting with DNN's getVars method, specifically the dnn.vars object.  Our temporary workaround was to set dnn.vars = null right in the constructor of the jquery widget, however we are hoping issues like this are addressed in future releases of DNN.

The offending code:

getVars: function() {
        if (this.vars == null) {
            var a = dnn.dom.getById("__dnnVariable");
            if (a != null) {
                if (a.value.indexOf("`") == 0) {
                    a.value = a.value.substring(1).replace(/`/g, '"')
                }
                if (a.value.indexOf("__scdoff") != -1) {
                    COL_DELIMITER = "~|~";
                    ROW_DELIMITER = "~`~";
                    QUOTE_REPLACEMENT = "~!~"
                }
            }
            if (a != null && a.value.length > 0) {
                this.vars = Sys.Serialization.JavaScriptSerializer.deserialize(a.value)
            } else {
                this.vars = []
            }
        }
        return this.vars
    }