New dhtmlxLayout changes document.body.className

I am using multiple dhtmlXLayout objects within a project
A “1C” layout is attached to document.body
I have attached a dhtmlxTabbar to 1C
Some of the tabs then have their own Layout objects attached.

After the 1C layout and all of the initial tabs are loaded, I edit document.body.className to add an additional CSS class (this is used for dojo and has no effect on dhtmlX).

When I open a new tab and attach a dhtmlxLayout directly to the tab, it is overwriting document.body.className
I would only expect it to edit the className for the div containing the newly created dhtmlxLayout.
Is this deliberate behaviour?

I believe the following function is causing the issue in dhtmlxwindows.js, as this.vp appears to reference document.body:

this._engineRedrawSkin = function() {this.vp.className = "dhtmlx_winviewport dhtmlx_skin_"" dhx_wins_rtl":""); ...