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What could cause this randomly appearing error inside jQuery itself?
this.element.find('.banner-btn')

Uncaught TypeError: Cannot call method 'apply' of undefined
makeArrayjquery-1.7.2.js:4858
Sizzlejquery-1.7.2.js:5110
jQuery.fn.extend.findjquery-1.7.2.js:5432

// Take an array of elements and push it onto the stack
// (returning the new matched element set)
pushStack: function( elems, name, selector ) {
if(window._debug_jQuery_pushStack) { debugger }
    // Build a new jQuery matched element set
    var ret = this.constructor();

// ---- the function continues, but this is enough for us ----

pushStack: function( elems, name, selector ) {
    // Build a new jQuery matched element set
    var ret = this.constructor();

    // temporary workaround for chrome issue #125148
    // http://code.google.com/p/chromium/issues/detail?id=125148
    if (!(ret instanceof jQuery.fn.init)) {
        console.log("applying pushStack fix");
        ret = new jQuery.fn.init();
    }

    // ... snip ...