DHTMLX will not work when embedded within SharePoint 2013

We have a sharepoint site with an iFrame to one of our DHTMLX based sites.

Suddenly the page will no longer render fully within the SharePoint iFrame.
The dhtmlxGrid will not load.
The DHTMLX page works fine when viewed through a regular iframe in a basic IIS site, but not via an iFrame in sharepoint.

This worked fine on sharepoint 2010, but seems to be an issue now that we are on sharepoint 2013.

I have reproduced the issue with the out-of-the-box dhtmlxgrid samples provided with DHTMLX3.0 Pro.

When debugging with IE11, it seems that when viewing the DHTMLX page within a sharepoint iframe, the line of code this.obj.rows[0].childNodes[i].style.width=this.cellWidthPX[i]+“px”; fails:

if ((_isOpera)&&(this.ftr))
var l = this._cCount;

	for (var i = 0; i < l; i++){
		if (this.ftr)

If I comment out the line, the grid will load.

Unfortunately, this fix alone is not enough to get the rest of our application to load, so I am hoping the above might help to shed some light on the underlying problem that is at the root of this new SharePoint 2013 iFrame + DHTMLX incompatibility…

Does anyone have any experience with this or know why the above line of code will not run within a SharePoint 2013 iFrame ?