IE7 crashes in two page view

[Edu Hackenitz]

When using release 29 the two page view button crashes in IE7 with a JS error
 It's on line 1980 : this.twoPage.reductionFactors.sort(this._reduceSort);
 First thing I tried was to comment this line and then it looked like it was solved...but I wonder what the functionality of this line represents ? Is it an essential part ?
BTW: don't not use the compatiblity mode of IE9->IE7 for this problem is not happening there.