Has anyone tried using said components together? When I try to run the HtmlEditor inside a InfoPanel I get an exception. Running the htmlEditor by itself works and the Accordion by itself also works, but combined, bad news
First of all, Accordion is user extension so Premium Help rules don't apply to it as it's not official Ext JS LLC product.
Nevertheless, I'll help you.
The most basic rule connected with Accordion/InfoPanel is to NOT render advanced Ext components (grid, tree and probably also HtmlEditor) into a collapsed panel. Collapsed panel is display:none so no dimensions are available.
Therefore I put all lazy creation/rendering of such components to panel's expand event (with option single:true).
Try to do the same to see if the problem persists.