As explained on http://my.opera.com/hallvors/blog/show.dml/1665828 : on limited platforms like mobiles, Opera's Function.prototype.toString does not return source code (due to the memory- and footprint cost of decompiling) so this part of the isFunction method will fail:

/function/i.test( fn + "" )

May I suggest adding the below workaround somewhere?

if( (function(){}).toString().match(/\\^[ecmascript/i) ) Function.prototype.toString = function(){return 'function'};